As far as I know, the show was never filmed in Widescreen (of any kind) until about two or three years ago. However, if it was, then the show would probably be in 1.77:1 (which is what most US widescreen HD-TV shows are filmed in).
Having said that, Warner's aren't exactly that good with widescreen TV shows. Remember the balls-up they made with "Babylon 5"?! And why do they still insist on using double-sided discs, rather than single-sided ones? The cheapskates!
I do have one query though: what about other Regions, e.g. R4 Australia, R2 Japan, or R1 USA/Canada? Are they also on double-sided discs? I'd much rather get single-sided versions, not double-sided ones, because there's less chance of scratched discs.