That is correct. The 6148-GE is first supported in Native IOS 12.1(19)E1 for the older supervisors (Sup1 and 2).
Neither the 6148-GE nor the 6548-GE is really positioned for the server farm. They're positioned for 'wiring closet' and 'premium wiring closet', respectively, possibly because they're both 8:1 oversubscribed, and likely because Cisco have something else coming up which isn't (that much) oversubscribed.
HTH,
-A
Asbjoern Hoejmark | CTO | CCIE #8525
Wingmen Solutions A/S | Gyngemose Parkvej 50, 1. | DK-2860 Søborg | Denmark
M: +4525162108 | E: ah@wingmen.dk | W: www.wingmen.dk