Question on correct number of outs.

[bocablkr]

The following excerpt was taken from Paul Philips Blog -

Next time barry was UTG he opened for 600 and was flat called by another player. I put in another 400 from the BB with 76o. After a flop of 7s6c4s I checked, he bet 1100, I moved it in. He didn't look real thrilled about it but after doing some calculations he called another 3500ish with T9o, thinking he had ten outs instead of four. I received my signed copy of his book. Man, it's HEAVY. It should be called "poker aces and back problems."

Excuse my stupidity but why is there only four outs? There are four 8's but wouldn't runner runner 10, 10 or 9,9 also be outs for Barry? How about 10,9? What am I missing?