There are different reasons why so many Names for Hash-m are used in the Tefilos, not only YKVK.

1. The Maharsha here writes that most Korbanos come to appease the Midas ha'Din (attribute of judgement) for transgressions that people committed. Therefore, logically it would have appeared to be more appropriate for the Torah to use the Names Kel and Elokim, which signify the Midas ha'Din, in connection with Korbanos. The reason why the Torah uses the word YKVK is because the other Names are also names of Avodah Zarah. The intention is to emphasize that Hash-m did not give any power to other forces in this world, so, consequently, when the Torah uses only YKVK in connection with Korbanos, it is emphasizing that we must worship only Hash-m as expressed by His special Name.

This idea does not apply to Tefilah, because the principle aim of Tefilah is not merely to appease the Midas ha'Din as atonement for our sins, but to arouse Hash-m's Rachamim (mercy) upon us. This may be derived from the Gemara's statement (Berachos 20b) which refers to prayer as "Rachamei"; prayer is a way for us to come close to Hash-m by seeking His mercy. This shows us that one aspect of prayer is that we seek to approach the Midas ha'Rachamim (attribute of mercy) and we are not concentrating merely on appeasing the Midas ha'Din. Accordingly, in Tefilah there is no "Havah Amina" that we are addressing only the Midas ha'Din, and thus it is possible for us to use all the Names of Hash-m.

2. I found that the Abarbanel, in his Introduction to Sefer Vayikra (DH ha'Perek ha'Revi'i) writes that the statement of Rebbi Shimon ben Azai is a support for the opinion of the Rambam in Moreh Nevuchim that the Korbanos distanced the Jewish people from Avodah Zarah and drew them towards the service of Hash-m. This is why "Kel" and "Elokim" are not used; these words are used, in different contexts, for Avodah Zarah. (This explanation is similar to that of the Maharsha in some ways, but according to the Abarbanel the purpose of Korbanos is to draw the Jewish people away from Avodah Zarah, while according to the Maharsha only the Name YKVK is used so that one should not think that the Korbanos we offer are similar to Abodah Zarah).

The Abarbanel cites another Gemara (Temurah 29a) which he says is similar to the Gemara here, and which is also a support for the Rambam. The Gemara there states that the verse, "My Korban... you shall guard to offer to Me" (Bamidbar 28:2), means that the Korban must be for Hash-m and not for "another master." The Gemara there stresses that our Korbanos nust be for Hash-m and not for Avodah Zarah.

The above concept is not applicable to Tefilah, because there is no reason to say that our Tefilah to Hash-m is to keep us away from Avodah Zarah, so it follows that we may use all of the Names of Hash-m in Tefilah.

Kol Tuv,

Dovid Bloom