I think the problems with 2 strokes has always been:
1) integrated fuel and lubrication systems, yes they work but the second they don't, bad things happen...on a 4 stroke, you check the oil, as long as it's clean and full you rarely have problems....
2) sensitivity to lean running which can cause rapid damage to pistons etc
Now with pre-mix engines were there is no oil injection to fail, as long as they are never straight gassed, I think they can last longer, like all my small engines, all of which are more than 20 years old, though I do have a 1987 3.5 Briggs 3.5 hp that keeps running just fine as well....