chance what though a spontaneous infection? if the keg sat around opened and unsealed I could see your point.
I really think this is dependent on the process and whats stored in them. there was a thread on this about a year ago and after that I started pulling my poppets to check them for a while after cleaning and preassure washing the poppets without disassebly.
Not once did I find any "gunk" if I dry hopped or didnt use the side valve on my conicals to keg from I could see things being different.
At the brewery we use a keg washer to wash our sanke kegs but we do not disassemble them there either. ive talked to brewery owners who actually just rinse and sometimes skip even that when refilling with the same beer.. Not something I would do but my point is the beer does not become infected with these pratices or they wouldnt do it that way right? it very well could have negative effects but it seems they arent noticable enough to effect practices at those places.
Nope, no infection(s).