I dont think download size does matter too much.
I wouldnt have a prob downloading a CD from the net. HTC could very well send out CDs for a buck each on which they burn the game. At least for the paying customer base. And nowadays almost everyone has a DSL or cable or whatever connection. There are only few who actually only have a 56k modem availabale, and they could very well get a burnt CD.
And remember: When AH was beta or just went open, the requirements were not low for that time! So I dont think they should stick to old gfx. You know, it worked to have good gfx back then. Why not today?
And the patches wouldnt be as big as the while game. Although a bit bigger maybe. But not so much that it would pos a real problem.
One problem would be though, that HTC would have to pay for this huge traffic such downloads would cause. And HTC does have to care about gameplay. Maddox Games does not and doesnt need to. You know, Il SP sucks because the AI is bad (always bad compared to MP) and MP is faulty too, spawn pauses, non-spawn-pauses, whatever. In this regard HTC is already way ahead of IL-2, I just dont know what impact such a souped-up gfx engine would have on the development.
The release of the tour of duty would be pushed back, be sure