Um..
I ONLY comment on phones that I have had experience with. Okay so lets not use my opinions. Lets look at specs. 53mm vs 46.5mm. There you happy?
Really though, if you've held both phones, I beg you to judge them HONESTLY. I've used a razr for over 1.5 years, and when i held the d600 it felt much more comfortable. But of course, my opinion doesn't mean crap. I guess the razr just magically feels more comfortable, despite it's slippery design and crazy wide structure. No problem with me, i guess some like it.
Now that we have appearance aside, UI is really opinion based. I assume you've used motorolas your whole life, that's why you are used to the UI of their phones. I've used SE, Nokia, Moto, most of the big brands out there. I really don't have a problem with any of them, they all work fine. I didn't say the d600's UI is superior, i'm just saying for 90% of the people it isn't a problem.
About modding. I have to admit i have absolutely no experience with actual hardware modding. But I assume that I wouldn't want to have the risk of damaging my phone, just to get features(right?) that already comes standard on another phone. I HAVE had experience with both phones, so no point in bringing that up again. I know YOU have had experience with both too, so I won't bring it up either.
Last thing, hey man it's all cool. I'm not pissed off or anything. It's a debate about phones, haha all good. =]