Well, Warner has stated that all their High Definition releases will be available in both formats (unless Blu-ray flounders, but I don't think that's happening anytime soon). For example when they announced Forbidden Planet and Mutiny On The Bounty, the news included BDs at a "later date". So it'll be a matter of time. BD player numbers are going up, so the demand will go up. Right now 32% of my titles are Warners (the majority) so they are getting great BD business concerning me. Titles look good, they know people will buy them.
One thing to think about is that Smallville on BD-50 would take only 3 discs, not 5. Maybe that's too obvious a format advantage to show early on?

If it were on BD-25, they would be 6 discs. So this factor may be affecting release time timetables. If the Disney "Lost" news are confirmed, wouldn't Warner pit a Smallville release as their TV series offering? Maybe Stargate CG-I (announced a looong time ago) will pop up then too!
I've watched a few Smallvilles in 720p. It looked close to a theatrical exhibition. the 1080p will twice better!

. I've actually avoided watching it cus I knew it be released on 1080p High Definition. I don't want Season 5 as bad as I want Season 1!