It's not about his preference of the UI, it's about his preference of phones that do not appear locked down. He prefers Nexus because of the stock Android UI (nothing to do with iOS UI here!), but even more he prefers nexus phones because Google is fighting the proprietary locked down carrier approach -- the one that makes us slaves to our carriers in order to get a good phone at a decent price. I may get a Nexus 4, and in that situation I can purchase my freedom from my current slavery to Verizon for a paltry $100. I can actually evaluate all the carrier options and determine which phone is the best. If this kind of freedom takes hold, it is likely that carriers will actually have to compete at some point, instead of customers being forced into one carrier their whole life (basically). Then other aspects of carriers will probably improve because they have to compete.

In other words: It's not a preference for one design over another, it's a preference for freedom. You may disagree with the freedom argument, but this is certainly what it's about. This is why Linus is coming out to bat for Android -- not because he likes Google or Google's style, it's a pragmatic decision because he thinks Google is his friend as far in trying to reintroduce competition into the market.