RedLynx sold more than 800k copies of Trials HD (as of March 2010) without much of a marketing support. That's an example. With 4-man studio you don't need nearly as many sales to break even, so that shouldn't be a problem for a really good game, should it?
The competition is stiff indeed, but that's a good thing for a players - we've got a lot of games to choose from, and don't have to buy garbage (of which there's a lot in XBLA), as there's always something interesting in each genre. But the thing is, it's usually just several good games for the genre (and rarely one great one), so you don't have to compete with EVERYONE - your game just have to be good enough to consider it among tons of trash.
So the reason for XBLA bashing is either they don't really believe in the quality of their game (and its ability to compete with the best of XBLA), or Sony gives developers some benefits for PSN-exclusivity, and these benefits looked better for the team, than potential XBLA sales.
P.S. Oh, and remember the fantastic Trials HD - maybe these guys just saw it and thought they've got no chances?
P.P.S. I haven't played Joe Danger - all of the above is just extrapolation.
P.P.P.S. 1.5mils for Castle Crashers, 370k for N+, 360k for Braid and Undertow with 625k. Are these all high-budget games from huge developers? Compare that to Shadow Complex with just over 400k sales, so you'd have the idea of how marketing and developer's size correlates with the number of copies sold.