#1: Well first of all, there never was a PS2 version of PSO, just that terrible spin-off. Secondly, the Xbox version really isn't worth mentioning, as it is completely integrated through Xbox live (and since it's not compatible with the 360, that means it can't be played online anymore, not even on a private server), doesn't have all the features of the GC version, and let's face it...This is the Xbox we're talking about here. It has the worst controller of the last 10 years, undoubtedly. So, again, it's really a matchup between DC and GC, and DC clearly loses that one. As for the DS version you mention, it's not even the same game...We're talking Phantasy Star Online: Episode 1 & 2, not some horrible portable spin-off with half the graphical capabilities and shoddy controls.
#3 I have about 5 friends who I play games with on a regular basis. I once spoke with them about the Dreamcast. None of them knew what it was, so I explained. The Dreamcast died in 2001, almost 10 years ago. Most "gamers" today, unfortunately represent ages 12 to 16, and none of them are going to know about a console which is older than they are. The fact is, the Dreamcast was a good console, but it was not a great console. I mean come on, let's be real here. I own a Dreamcast, and I've had fun playing SC, Rayman, Sonic Adventure, etc. on it. But when it all comes down to it, it's not a very good console by today's standards. Sure, it had some online games, so did the SNES, and the Saturn, and the N64, and the Genesis before it. Are you seriously telling me that the DC's library "trounces" the PS2? Have you gone mad? The DC has about 8 really quality titles. The GC and PS2 have more along the lines of 50 and 150 respectively. And yes, it does wreak of obscure titles. Almost no one knows about Rez or Ikaruga or Dynamite Cop. It's a very old console, and it's one which never made it past its second year, didn't sell very many games, and didn't sell very many consoles. Don't expect people to know about it, because they wouldn't, and they don't.
#4: That kind of just reinforces my point then, doesn't it? Reviewers are, for the most part, payed jackasses who sit around, play a game for 3 hours, and then either be overly or underly critical of it. If everyone thought what reviewers thought of a game like SFA, it wouldn't have sold a million some copies. What really matters is what players think, and players think of it just fine.
#5: Again...I'm not saying sales are the ONLY factor, but they are a contributing factor none the less. As I mentioned, you have games like Eternal Darkness which are just brilliant, but they don't sell well because they had no promotion, or in some cases, most people will just find them too hard. Overall however, any game that gets both bad reviews and has bad sales, is- yes, a bad game. Star Fox: Assault, as an example, got "bad" reviews, but had great sales, and great reception by gamers, and therefore is not a bad game.
BTW: Why are you using Ico and SOTC as examples of games that sold poorly? SOTC sold 140k copies in its first week, and has sold 940,000 worldwide so far (and it's still being produced might I add), Ico has sold around 700,000, and sold around 110,000 it's first week. That's pretty good, especially considering neither of them really had any advertising to speak of.