Right now while downloading my first Let's Play videos I'm asked myself about how my high the resolution should be, how long and detailed the playthrough should be etc. After all, I'm filming the content of stuff one usually needs to buy in order to see it actuall running (especially if there's no gameplay video provided by the publisher/developers). Personally, I only watch Let's Plays of games I suck at (having not fun playing it myself), games I can't play (not having the hardware) or just because I like the commentary. Thus, I'm either owning it, want to own it or never had any interest playing it.
Uploading long and detailed (sometimes even interactive) Let's Play in HD does sort of give people the ability to see everything without buying it. If a game's gameplay sucks, you can still enjoy the graphics by watching a Let's Play without wasting money. Doesn't sound wrong, ey? Well, this is true for random Youtube visitors. Bigger publishers want to prevent users from not buying their super-linear games because that's the only way to get any value out of it. But even with a complex and big game where no player will have the same experience, spoiling certain quests or parts simply either destroys buyability or replayability.
I won't try to "protect" a developers/publishers plans of getting as much people as possible to buy their games while not giving them proper gameplay video. In the end, I use Let's Plays to inform myself whether a game is worth buying or not. Thus, I stop watching Let's Plays if I want to (and can) buy a game. If someone fails to advertize a game good enough, Let's Plays are the best way to get a good gameplay experience right from an everyday consumer. Therefore, I'll just record as much as interesting to me and in the whole project. Not in high resolution of course. I'm currently recording at 840x524 pixels with quite visible artifacts. I don't care about giving too high visual quality since I think Let's Plays should be watched in the background and not as a main entertainment source. You can still buy the game if you want high quality, you know.