Yep. In 5.1 etc the centre is considered the most important speaker as it carries most of the soundtrack, primarily the vocals. The sub does just that, just the sub stuff, I used to run two subs in a 6.1 set up, I've since dumped both and my centre rear, and let my floorstanders handle the low end and actually prefer the more 'together' sound.
That said after spending ten years as a richer sounds manager and having escaped I'm rather less picky these days than I used to be.