That makes sense for the 9220, as it's a very low end 2G-only phone (retail may be less than $200 USD) that is designed for economy markets. I can imagine this being one of RIM's most popular handsets internationally, but not in countries where EDGE is being depreciated.
But as for the 9790 and 9380: Both of those have been available in Canada for a long time and are actually quite nice (though admittedly not as popular as the 9900 or the 9860). These, being slightly-lower-end versions of the two handsets I previously mentioned, are simply being passed over. Contracts reduce the prices of phones, making expensive models more obtainable and these cheaper ones not a super great bargain. Looking on Telus's site, the 9380 and the 9860 are both $0, while the 9790 is $80 and the 9900 is $130 (and the older 9780 is free on a shorter term)
I just bought a 9790 yesterday as replacement for my aged 9700. The 9790 is a great successor to the 9700 especially if the 9900 is to big for you. The 9790 gives me much more the "9700"-feeling than the 9900. I feel sorry for you US people not being able to buy this great device - greetings from Germany.
I was wondering why the 9790 doesn't seem so popular. It's a great little phone, the 9900 was too big for me to easily handle so the 9790 was the way forward. It's a shame the USA is going to miss out on it