The Kollel wrote in Background to the Daf-
>>(b) [line 22] L'INYAN HECHSHERAN - with regard to their ability to cause Hechsher l'Tum'ah (HECHSHER / KI YUTAN)
(b) The food can only become Tamei if the owner of the food was pleased that his food became wet...<<
Isn't this "al zeh anu danim"? The whole point of whether it's considered water or wine determines if the hechsher needs to be leda'ato (water) or not (wine), isn't it?
There are two times when Ratzon can affect rainwater: (a) If the water falls onto fruit b'Ratzon, it is Machshir them. This is true of wine as well. (b) Rainwater that falls on the ground is not Machshir. (This is known as "Mechubar"). It is only Machshir after it is removed from the ground with b'Ratzon . This is known as "Telishah b'Ratzon." (Once there is Telishah l'Ratzon, it may not be necessary to have it touch the fruit b'Ratzon, see RASH beginning of Machshirin.)
As far as the Ratzon for touching the fruit ((a), above), there is no difference between water and wine (as Tosfos points out, and the Rashbam might very well agree). The difference between them is that rainwater needs Telishah l'Ratzon ((b), above); that is, as long as water was not "uprooted" from the ground l'Ratzon it does not have a "Shem Mashkeh," whereas other Mashkim get their "Shem Mashkeh" without Telishah. (That is, other Mashkim are able to be Machshir even though they are "Mechubar").