Simpler in-line SDLV

I havent seen this idea, so here goes:

Take one traditional side mounted SDLV.
Get rid of the ET's LOX tank.
Replace the cargo can with a Delta IV hydrogen tank, modded for LOX.
Stage II and the payload go where the old LOX tank went.
The intertank becomes the interstage. The stack gets a lot shorter
that the ATK proposal, and you dont get the off center thrust of, say,
Zurbin's Ares.

The launch pad remains the same.

Now there must be a reason why this has not been seriously proposed -
any thoughs?