There's never going to be an exclusive COD, NFS, etc, on NGP.  From what developers are telling us, Sony's even selling the system to them as a handheld that can run their PS3 engines... the only way it's going to get any exclusives, rather than ports, of the big western IPs is if Sony bankrolls them directly.  It just doesn't make financial sense for western 3rd parties otherwise, when they're looking at a more limited market than 360/PS3 for the same level of cost.  For COD I could maybe see something like a "Modern Warfare Collection" for launch, essentially an "exclusive" repackaging (that could even be farmed out), but it's not going to get something like an AAA exclusive COD effort.

As far as Japan, PSP's riding on a high right now, but the platform's dead elsewhere.  Games like MGS or KH, games that should easily clear 3-4m worldwide are looking at sales likely half to a third of that... when you combine PSP's western failure with NGP's explosive budget increase, you're looking at a relatively risky platform.  From a Japanese perspective, it's also a platform that more or less hinges entirely on what Capcom decides to do with Monster Hunter, which has to be a bit of a worrying position for any 3rd party deciding now where to invest development for the next few years.  3DS by comparison is a more lateral shift in terms of resources (companies can just bring their PS2/PSP engines over directly, and expect similar budgets going forward), plus Nintendo's now taking a more active role in courting 3rd party content early on... I mean we're already seeing developers and publishers that previously looked to be favoring PSP (SE Osaka, KojiPro, NIS, imageepoch, Namco, Capcom, etc) moving pretty strongly into 3DS.  Honestly, I expect 3DS to get even better Japanese support than DS did, and at a much quicker pace.  It already has really, there's not going to be all that much space left for NGP, and even in Japan I think you'll see a lot of developers simply porting 360/PS3 stuff.

As far as the others you mentioned, Epic's already on board in a big way (UE3 seems pretty central to Sony's NGP strategy) and I could easily see Valve or id join in too.  Epic and id have been big iOS evangelists though, I don't really see NGP support as too big a shift for either since they've been getting into handsets for awhile, it's more a natural inclusion for their multiplatform support.  Valve could be big though, but Valve tends to be a more cautious developer (look how long it took them to start really investing in PS3).

Yeah games are definitely important. It really needs that big killer app that can sell systems (DS had Nintendogs as a new IP killer app, then old massive hits like NSMB DS, Pokemon and so on). Basically PSP never did have one of those if we look at its software sales, the closest was the GTA games.

And now in the last two years PSP is just JRPG heaven (thats why I re-bought one after being initially disappointed).

Neither 3DS nor NGP have interested me that much so far, neither are on my to buy list, especially not with the way PS3 and PC (especially PC games line up is so awesome for this year) line up is shaping up this year.

 We'll see. I fully expect to see some sort of exclusive COD (Why else would Sony have lead their NGP software announcement with it?), simply cause Activision are furthering that brand everywhere possible, and they'll make more money off a unique NGP game then just trying to sell more copies of the game already on PS3 / 360.

Sony have absolutely not sold the system as something they want just ports for, and if you've bothered to read any of the developer commentry on the device it's been the complete opposite message. Sony want unique content and that's what they're pushing for (Check the thread from here a few weeks ago... was on the Sony forum though I think).

 And again we've someone who is inflating the NGP's developement cost with no possible source and no possible idea what the thing will cost (Find me a link to say the NGP dev costs the same as a HD console, or as an analogy, that the PSP costs anywhere near the PS2 lol). Sure it'll probably be more then the 3DS's, but the games will probably cost more too, and it'll have a bigger share of games sold via digital distribution, so hell it could end up more profitable for publishers. We can both speculate either way, but truth is, we don't know yet. The one thing we do know, is that every developer who's commented on the device has been positive and that the NGP is extremely accessible for developement and positioned great for anyone who've worked on the PS3 or 360, whether that be ports or just resuing engines / middleware / assets to make new games for less.

 Until E3 we're just speculating on what the NGP will have anyway. Sony's list thing from January had pretty much every publisher on it though, so everyones working on something for the thing. I don't view the NGP having any software trouble near launch, it's whether the thing can sell that software that'll decide if it sustains alot of support.