Not really, having one exchange alone controlling more than 80% is as centralized as you would like.
What would happen to bitcoin if mtGox was shutdown overnight.
Other exchanges would gain marketshare.
Now compare that to what happens "if" LR gets shutdown overnight.
Nobody is saying a major exchange closing wouldn't be disruptive but with a centralized currency it is a complete failure of the network.
BTW: MtGox marketshare has been declining. Over last 7 days it has been 66% of the major exchanges.
http://www.bitcoinity.org/markets/list?currency=ALL&span=7dOf course that 66% excludes other exchanging methods like OTC.