I believe most of the 30s you see without the rail will be 2nd gen? 3rd gen started the rail but i'm not sure if you can buy a 3rd gen w/o the rail.
While some would argue that it's not the most tactically (sp?) sized glock, the rails are great to have if you want to throw a weapon light or something on there late one night if you hear someone downstairs.
I've had 3 glock 30s - best glock made in my opinion. Great size for concealment, holds 10+1, great stopping power, most accurate glock i've shot (for my shooting style.. though many agree).
Hope this helps!
Rob