I think you have the Bitcoin pizza story mixed up. Laszlo did not exchange $10,000 worth of Bitcoin for pizza instead he exchanged 10,000 Bitcoins for the pizza. At the time the 10,000 Bitcoin wasn’t even worth up to $50. You can check the post here:
https://bitcointalk.org/index.php?topic=137.0. Also, I don’t think that the person who got the 10,000 Bitcoin still has it. It’s possible but the chances are really slim because Bitcoin merely being $1000, that’s a lot of money that the average person may want to have cashed out.
There is many accounts which hold a big amount of Bitcoin on it. Some of these accounts have an owner which died, lost the keys to open it, holding for a better price, companies using it to avoid taxes and so on.
Laszlo spent a big amount of Bitcoin for something that worth it at that time and which doesn't worth it anymore. I would buy a normal pizza right now for 0.00045 Bitcoin which is equivalent to ~$20 but I will definitely cry it next years when I see that I bought a pizza for ~$200 or even more.
Well, I didn’t say it’s impossible, I’m rather saying that for the person who got the Bitcoins from Laszlo, I think the chance is slim that he didn’t use it already. The fact that he even wanted and made the trade with Laszlo shows that he saw value in Bitcoin and knew what he was doing. It’s not like he just carelessly did it. So, even Bitcoin at $1 was already a tempting time for him to sell. I’m assuming he was also skeptic if Bitcoin price will go back down. That’s a lot of gain to not be tempted.
But let’s think of something, how about Laszlo himself? To spend 10,000 Bitcoin, he must have had a lot more (I assume)… how about him then?