Does this make the bitcoin ultimately usable as a worldwide currency, replacing current currencies?
I think not, and it's built-in.
lol, question talker...nobody likes them.
also...get your facts straight.... read:
http://bitcoin.org/bitcoin.pdfsecret hint: each bitcoin can be devided by 10^8 ....now please do some more fancy calculations
Just teasing

... No, actually I was just worried to death that a bigtime failure was built in.
But let's get back to the facts indeed: then 1 micro bitcoin / USD makes BTC 1 / 10^8 = 1 dollar cent.
That means... yehey!, you're right.
Doom and destruction aren't neigh!
Ok, so the dollar cent is hiding inside the smallest possible denomination of the BTC.
Now, either this is an ingenious hint of premonition regarding the utmost stability of the BTC's value, or still 1 or 2 orders of magnitude short.
In my opinion it is the latter.