An LCD has a huge single point of failure - the LCD driver, and (if applicable) the backlight and its inverter.
Most laptop or flat panel display failures I have seen were in the LCD backlight or the driver, and the loss of use was total. In fact I don't recall ever seeing any other kind of LCD failure.
Obviously, a failure in the OAT sensor or its interface will still affect just that one feature - same as with conventional avionics.
The are ample stories of the whole glass system crashing and resetting, and one of them (Avidyne I think) was at one stage not resettable during flight. Stuff like that will contribute to depreciation once the word gets around...
Glass cockpits were a huge opportunity to solve the main reliability killers in avionics - moisture and vibration - but neither have been addressed. The first one was wasted by having ventilation slots in the main box (because they didn't design the thing for low enough power; another story) and the other was wasted by generally commercial construction. So I don't think that long term reliability (10 years plus) will be any better than old style avionics (ignoring old style avionics that were truly crap anyway, e.g. Narco, and some other stuff that is simply a crap design, like a certain autopilot I know about
). And one will have more eggs in one basket. The best bit is that only an authorised dealer can repair the stuff, because Garmin etc are keeping the manuals very close. They learnt a lesson from the freely distributed PDFs which ended up all over the internet and which enabled every street corner freelance avionics man to fix the old stuff. Can't do that with the new stuff. It's a flight back to RGV or whatever, every time. The same old avionics shop line: "Drop in to us, Sir, and we will have a look at it". £300 for the trip, plus hotel, etc. Great stuff. That's why I prefer separates (not necessarily steam gauges; just individual removable electronics like e.g. a Sandel EHSI) because one can order an exchange unit and do a field swap, with zero downtime and zero flying around to dealers.