I am not getting something about this subject.
Seems like this subject only appies to the Galaxy Tab (and maybe the Xoom, just released).
The only other tablets with 3g are the Dell Streak (and I would seriously consider one if it were offered by Verizon), and the Huawei S7 (although it seems to be difficult to get on a GSM-based provider, esp T-Mobile, although not so problematic on AT&T per
http://www.androidtablets.net/forum/huawei-tablets/ topic postings, so most users are "getting by" with wifi only, and it costs $300 at Best Buy "normally" - 249 this week).
Most other tablets discussed on
http://www.androidtablets.net/forum/ seem to be wifi only.
Maybe they are "rare" because they keep selling out as with the wifi-only Archos 101 and 70 tablets (under $400, or less for smaller sizes), and the Nook Color ($250). Enjoying my wifi-only Archos 5 Internet Tablet ($125 open-box closeout at Best Buy, but that is an exceptional situation).