There's plenty of senn users over there who also come here. Marcus is just a guy who likes particular headphones as I see it. I actually came from a darker pair (DT770 pro 80 ohm), and was converted to the "bright side" after I acquired a pair of etymotic headphones from a friend who no longer needed them. I happen to know one of the moderators (bioxeed) still uses DT770s.
As for the grado/AT recommendations, I think it has to do with his average customer - who is going to be plugging straight into a soundcard. IMO he's right about the MS1 and AD700 being the best buys around the HD555 price bracket.
For what it's worth, I believe he actually doesn't like stax (or rather he's made jokes about it in the past), so anyway.
IIRC further, the Aus senn dealer is a jerk (he can't list HD800, HD600, HD650) because he has a website, despite having them. He's also mentioned something about getting more returns for sennheisers (possibly due to the soundcard issue mentioned earlier). Senn isn't as good a buy here as it is in the states IMO. I mean, local prices for the HD800 are still what, 2000 USD? IIRC the T1 is only 1300
But anyway. Interesting note, he's getting LCD-2 stock, which means Aus will have one of the first(?) stores that let you walk in and try the LCD-2 before you buy. The forums are fun to go there (IMO the community is a little more friendly than head-fi - well a lot more relaxed, put it that way), and I think his business ethic and the way he presents himself would make up for any disagreeances I have with him (for example, I dislike the MS1).
But take this with a grain of salt I tend to agree with Marcus on what sounds balanced, what sounds fun and what sounds dark