Why would you have any burn in with a RPTV? Its just project light beams onto a tranlucent screen. So wheres the burn come from?
I'm not sure of the particulars, but suffice to say it's not just a translucent screen. It's also known as phosphor burn. Day-traders get it because they watch those stock-reports all day long. I see it in bars where the TVs are tuned to ESPN all the time, etc. From what I've read in PC Magazine the burn-in issue has gotten better on the plasma sets but still exists.
Here's an informative plain-English write-up on it:
Burn-in has a double meaning. The term "burn-in" has found it's way into HDTV and HD-ready TV language as a negative. It means that an image can permanently burn into the screen. It would be like a faint stain on the screen. The most likely paths to burn-in are watching a 16:9 TV in 4:3 format, keeping the TV on the same channel such as a all news channel with a bottom information bar or stock report channel and video gaming.
How does this occur? As an example a news or stock report channel can have an information graphic at the bottom or side of the screen. This is a static image and for the most part it doesn't change except for the text information. The shape and size of the bar remains consistent. If the TV is left on that channel consistently over a long period of time for months on end then burn-in can occur even if the TV is on for an hour or two a day.
An analogy would be similar to the living room carpet. If you walk the same exact path across it every day...even just once or twice...eventually you are going to leave an imprint of your path. By walking the same path you wear out that section of carpet. A static image consistently on the screen will not wear out the screen so much as IMPRINT that image onto the screen.
When you flip to other channels you'll see the ghost of that shape and it's always there.
All CRT direct view and projector TVs can be the victim of burn-in as well as Plasma. Plasmas are more susceptible. DLP TVs, LCD Flat Panel and Projector TVs and LCoS TVs are immune to burn-in. Don't run screaming for the remote every time someone tunes in CNN or plays the occaisional video game but be aware that if you leave a CRT based TV or Plasma parked on the same channel 24/7/365 or play the same type of video game with the score parked in the corner or an HUD then you could find yourself victim of burn-in.