Why is there so much variance in the mining?

[mustyoshi]

It seems like every time I check blockchain.info there are groups of blocks found within 30 minute blocks, and then there are times when it takes 30 minutes for a block to be found. While it still averages (according to blockchain.info) to be under 10 minutes per block, it certainly isn't that consistent.

And will this variance just get worse as the difficulty rises?

[cdog]

Do the maffs bro:

http://en.wikipedia.org/wiki/Variance