Hi!
I believe the side press demonstrated by Pavel in "The Russian Kettlebell Challenge" is both inferior and superior to the clean & press depending on your goals. Although the SP works your side muscles and lat more, it demands more flexibility and balance. It also lacks the "tight-to-loose" sequence - a goody that is safer for the back and useful for many athletes.
There is probably more differences to point out, but C&P being the most newbie-friendly press in addition to the carry over effects due to the "tight-to-loose" sequence is probably enough.
But the main reason is probably Pavel's many quality programs - they often favour the C&P. (Following a well designed program guarantees better results than putting something together by oneself if one lacks experience. That was my conviction when I started out training and I suppose others agree).
Best regards, Henke in Sweden