good first post.
Yeah, the 7621 and 7421 are both japanese-made. You get a slightly better bridge on the 7621, but that's a pretty easy mod for the 7421, so not worth worrying about, imo. There's the pickup difference, too, but while the New-7's are clearly better than the V7-7 and V8-8 (not knowing they were Dimarzio's, my first thought playing the 7620 I bought was "damn, Ibanez really got better with their pickups), you're probably going to want to swap them out for a better set eventually, anyway- they were a bit low-heavy for my ears, great for rhythm, but the air norton/tone zone set I've got in there now is much better for lead, IMO.
I actually got a chance to play a Squier Stagemaster 7 in a guitar shop near where I used to live- suprisingly, it was a decent guitar. It wouldn't have matched up to my 7620, but it didn't sound half bad, played decently, and the "fun" factor was much higher than the price tag would have led me to believe. I should have bought it then and there, as it was gone the next time I went into the shop ad it'd have made a great backup 7.
Of course, Squires are notoriously variable from guitar to guitar- sometimes you get one that can hold its own with most real fenders, while others are just junk. Play before you buy, if possible (for all guiars, really, but especially here).