I couldn't figure out what the gemara was asking on Rava from all the diyukim in the mishnayos until I saw your parenthesis (rava according the the first version). How did you know that and why does the gemara take it for granted after the question on rava on daf 17b specifically asked according to one of the lishonos?
Maybe the answer is simply that since the gemara's first question went through all the possibilities of the two lishonos before asking the question the rest of the questions rely on that framework.
BTW This is the first time I looked at your website. I was actually hoping
to find the answer to this question. In any event thanks for my most
productive lunch in my working career. i went through galei masechta on the
first perek. Actually goes quite good with a turkey sandwich!
D. Weiser, Rishon Letzion, Israel
Your question is why the Gemara does not state explicitly that its question is only on one of the Leshonos of Rava or Abaye (as it did with the question from our Mishnah, on 17b). This question actually applies only to two of the Gemara's questions. It applies to the question from the Tosefta of "Sela ha'Ba b'Yadayim" (which presents a problem for Abaye only according to the Lishna Basra), and to the question from "Marchikin ha'Ilan Min ha'Bor" (which presents a question on Rava only according to the Lishna Kama, which maintains that Rava prohibits digging next to a neighbor's field even if the neighbor's field is not designated for digging pits). The other questions on Rava indeed apply to both of the Leshonos of Rava, since they are based on sources which permit the construction of a Mazik that damages walls , or hinders plowing , etc. -- things for which every field is normally used.
In fact, these other questions of the Gemara may even be asked on Abaye, according to the second Lashon of Abaye, since that Lashon holds that even Abaye prohibits construction of a Mazik in such situations (as Sefer Marei Mekomos of Rav Karelinstein points out). However, since Abaye can avoid the question according to one Lashon and Rava cannot, the Gemara considers them to be questions on Rava. This is the intention of Tosfos (17b, DH Marchikin) when he says that the question from "Marchikin Es ha'Gefes" is on Rava .
We still must give reasons for why the Gemara does not state explicitly that the two abovementioned questions are only according to one of the Leshonos. As for the first one ("Sela ha'Ba b'Yadayim"), according to Rashi's Girsa the answer is clear: The Gemara did not bother to delve into the question at length (and to look for ways to avoid it without resorting to a new answer) because the answer was so obvious. In fact, as soon as the Gemara answers the question, it asks why the question was asked in the first place, "Why didn't the questioner think of this obvious answer?"
According to Tosfos' two Girsa'os, the Tosefta that is being quoted appears simply to be adding a point to the Mishnah. Since it is just an additional citation of the Mishnah's case, it is not necessary to spell out to whom the question pertains; as you suggested in your question, the Gemara is relying on what it already asked above from the Mishnah, and it already explained to whom and how the question pertains. (EINAYIM LA'MISHPAT, by the way, speaks out that the Gemara's question is only according to one of the Leshonos. Specifically, he addresses the second Girsa of Tosfos, which maintains that the question is on Rava, according to the Lishna Kama.)
The reason the Gemara does not say "Bishlama" with regard to the other question ("Marchikin ha'Ilan Min ha'Bor") is more complicated. The simple approach is that since it did not have a "Bishlama" in the list of questions that preceded it, it dropped the "Bishlama" here as well. Alternatively, perhaps even according to the Lishna Kama, Rava prohibits planting a tree next to a field that is not used for digging pits, since the roots of a tree actually enter into the land of the neighbor (which is not the case when one digs a pit next to the property of a neighbor).
However, there may be more to it than that. Rashi seems to have been bothered by your question, and to have presented an original answer.
Rashi (18a, DH Ta'ama Mishum Avodas ha'Kerem) writes that when roots from one's tree enter the property of a neighbor, they damage by interfering with both the digging of pits and the plowing of the soil. Why does Rashi add that roots interfere with plowing? Not only does this create problems (as the RAMBAN there asks on Rashi), it does not seem to add anything to the explanation of the Sugya. He could just as well have said that roots grow downwards and do not affect that topsoil that is plowed (as the Ramban there, and the Rashbam on 99b, DH Kol she'Ken Not'am, explain). Also, the Mishnah cited later on this Amud says that one may not plant a tree near his neighbor's Bor , implying that the tree only damages a Bor. Although Rashi might learn that the Mishnah means Bor or plowed land (and it is teaching that roots also damage a Bor), why should he adopt such an unnecessary explanation?
The answer might be that Rashi was bothered by your question: Why was the question from "Marchikin ha'Ilan Min ha'Bor" not preceded by a "Bishlama?" His answer is that even according to the Lishna Basra, and even if the neighboring field was not used for digging pits, Rava would prohibit planting trees next to a neighbor's field. Trees hinder plowing, and every field is normally used for plowing!
I that this was helpful. Take care,
Kollel Iyun Hadaf