That makes no sense. Odds are calculated using all the cards you can't see. You see 5 cards, out of the the 47 you don't see, 4 of them are 10s. Your chances are 4/47 on the turn, plus 4/46 on the river when you don't hit on the turn. If you're going to start assuming that people have 10s in their hands, then you have to start reducing the number of unknown cards you're calculating your odds on, and therefore the actual percentages stay the same.

Let's say there's 9 additional players at the table. That's 18 cards. The odds of each of those cards being a ten is exactly 4/47, so on average, (4/47)*18, or 1.53 cards, will be tens. So that means that there are only 2.47 tens left. But that also means there are only 29 cards left, so our odds of hitting a 10 on the turn are now 2.47/29 - which is exactly the same as 4/47.

Let me also say that I don't think this is what Ripptyde meant when he said that. Just clearing it up for some other folks.

-Fishmagician