GOW was mainly short due to time to develop assets, etc. and polish levels in that kind of game today.
Of course in principle more space does help but more for variety - i.e. a GOW level itself isn't that big, its the textures, etc. that are big but they are re-used across levels.
GoW2 can be longer and simply span disks if space is really needed.
The difference with BR (ignorning the PS3) link is that sure, if you're game needs 2 or 3 DVDs it could be a single BR - but BR doesn't make games longer, the developers have to do that.
As HS and Uncharted show games on BR can be just as short as GOW - although they may have more textures, etc. I suppose.
Funnily enough that's one of the things I liked about RFOM - it was overall a weaker game than GOW but it was waayyy longer in SP, reminding me of playing games like Unreal back in the day when the levels never seemed to stop coming.
The issue is also that many FPS players (whatever they say) clearly see MP as the main element so we're getting shorter SP (COD4, GOW, etc) balanced with a lot of effort in MP vs more effort in SP side of the game.
Obviously I'm not in that camp and would like to see much longer SP elements for my money but I'm not going to hold my breath - although RFOM2 I suspect will have a fairly long SP again.
Try to be reasonable... its easier than you think...
