a bit controversial but I'm not sure the answer is quite as cut and dried. I would certainly agree that if you've got a centre it really needs to match with your L&Rs. But... do you really need a centre?
bear with a me a bit on this as it goes against a lot of the standard thinking on this topic!
Last year I got some pretty good main speakers (totem arros, about 1k a pair), now due to all sorts of changes and upheaval (including moving house) my system has altered a lot in that time. currently I'm using a rotel processor and my arcam a90 as a power amp. this sounds absolutely fantastic in stereo. I powered my centre speaker using the aaron power amp I bought a few years ago. the thing I've found is that I'm not really sure I need a centre, the speakers in my room are not that far apart and at the same level as my plasma, they sound so good that I prefer using them on their own rather than mixing in the non-matching and distinctly cheaper centre. I am able to go VERY loud with this system, especially since the BK sub is taking care of everything below 80Hz (100 for music) and it doesn't sound at all strained or confused.
I'm not saying this is the case in all instances but, if your main speakers are fairly close to eachother (and sound good for stereo music) then maybe, just maybe, you'd be better investing more in them than splitting the cost between three speakers.
just my thoughts after a fair bit of messing around.