Thing is, it's easier to do streams on Twitch than making Let's Plays on YouTube. For Twitch, you just need the capture card, and program to stream really, and the new consoles make it easier to stream. For Let's Plays you need the capture card, but you also have to do the rendering, editing, etc. Really I chalk it up to cynicism I say. Mainly for some people there are those who do put enough time and effort into it that really deserve the money, and then there are people who you can tell who just do it for the money.
The other thing is, people seem to think that you instantly make a lot of money by simply putting a video up or streaming, when that is the stupidest thing ever. It actually takes time and work to actually get to the point in which you can actually make money (a little luck helps too). For YouTube I've seen some people think that 1 view equals 1 dollar, and I just laugh. One view on a YouTube video, or more specifically the ad, is about 1/3 of a single penny, and it fluctuates as well. Now when you get paid, you don't get that whole penny by the end. No 40% is automatically taken out and given to Google. Then the next amount that's taken out is from your Network that you are a part of (Polaris, Fullscreen, Normal Boots, Hidden Block, Machinima, etc.) and that depends on how your contract is set up so they can get anywhere between 10% to 50% of the remaining revenue. The remaining amount is given to you, unless you're doing Nintendo games in which case Nintendo is now taking a part of the remaining amount as well.
I've been doing LPs for about 2 years now, and it always irks me when some think it's instantly easy money. Easy money is a myth, it doesn't exist really, and if it did it won't last as long.