I used to differentiate between these in my reviews. I called this external durability vs internal durability. Not always the same as what you are discussing, but it is the internals that fail most of the time.
There was a period in time where Super Soaker made incredible tank like construction on the outside, but the insides were crap; particularly the max d valves. I actually have 2 Aquapak Devastators, my preferred sidearm of choice. You'll note that I did not list these in my Little Creek thread or in any previous war thread. I love them, but I haven't brought them to war because I'm afraid the Max D mechanism will break. If we have more time I'd like your help in d-max-ding them and seeing if there are other ways to ensure they don't fail. Actually, if we can get Ben and Scott involved too that would be great. Y'all are pretty good at repairs and modding to prevent breaks.
Half the screws on the Devastators already went bad, so I quite literally had to rip the plastic apart to get it open. I can close it back up and fire it, but it doesn't look pretty. I have said this before, but I don't think people get how serious this is - replace the stock screws as soon as you buy the blaster. My plan is to epoxy the cracked pieces so it doesn't look so crap, drill out the old screws, and replace them with new screws. If you want a real blast from the past, GNG used to advocate that you disassemble your blasters regularly to dry them out, clear out any rust, oil down parts with proper lubricant that won't corrode, etc. I think we should all do this much more often than we do currently.
My hope is that the newer WW guns are durable and reliable. Buzz Bee got criticized for using inferior plastic for a while, but I am more concerned about valves rusting out, etc. My Blazer's ball valve finally went bad, but when you consider the age of the blaster it's not really a surprise. Especially since I could never get it open to clean since *ahem* the screws were rusted out. Notice a pattern here?
Beginning with the WW Charger the quality of their internal components has improved. At least in my experience. I have 4 new Python 2s, well, new from last fall. One reason I purchased them wasn't because I was lacking in light primaries or that they were superior to my XP 310, SC 600, etc. but simply because they were new. When you buy a new blaster you can take out the old screws and replace them. That way you can clean out your blaster after every battle.
We definitely want increased reliability, but part of that is up to us. We need to up our cleaning and maintenance game.