There are different ratios of widescreen.
1.85:1 and 2.35:1 are the most popular.
1.77:1 (IIRC) is the ratio of widescreen tv shows and widescreen tvs themselves.
Apocalypse now was in 2.1:1 when it was originally released (it might be 2.35:1 now though).
All depends on who makes the films. Spielberg tends to go towards 1.85:1 whereas Kubrick went for 2.35:1.
Widescreen tvs tend to be made for the lesser widescreen modes. If they were made for the 2.35:1 ratio then you'd have black bars at each side of the screen or you'd zoom in and miss out on the top and bottom of the screen.
You can blame tvs for being popular so cinemas went to a widerscreen to try and pull in the punters. There was no standard ratio for widescreen back then as it was a developing system.
Some preferred 1.85:1, others 2.35:1. Both of them (and the lesser ones like 2.1:1, 1.77:1) were popular enough to be used throughout the years.
I suppose you can blame Panavision etc for not getting rid of the less popular ratios :-P
We've got a widescreen tv and what really annoys me are the non-anomorphic dvds out there.
