my guess is because theres lots of stories or rumors about how awful it is dealing with microsoft and you dont really get that from sony
Regardless if its the same on both sides, its a perception thing. Having Blow at the PS4 conference was a big deal for the indie scene, indie game the movie has scenes of team meat watching their game launch and not get the front page splash on xbox live like they were supposed to, Fish being all "if I put this on fucking PC i could have patched it whenever I wanted for free" are all negatives for the MS indie image. Not to mention when Super Meatboy went to PC they instantly started talking about how much better the sales were in a smaller amount of time compared to the 360 issues they had.
the RCR guys talking about how building his game on the Vita was a dream and how every indie studio should do that, Sony giving top billing to Journey and Flower and putting indie games into PS+ just helps boost their image on that front