I think there are many factors that cloud this issue over. And there are more important factors than how well they're built - mainly maintenance, care and use.
BUT, I believe many things are not made today with as much reliability and long life today as they were in the past. There are exceptions, and everyone will be quick to point them out. Andy was right in saying we only here about the survivors, not the many that were trashed.
However, our society now wants cheap, new things the whole time. In general (bar many people on AS and the like) people don't want something fixed, they want it new. So there's more demand for cheap products than high quality expensive ones. Most people live in densely populated areas so can 'pop down' to a shop when something breaks (again, exceptions of rural communities). Pros want a new saw every year cos it's cheaper than there time pissing about with an old one.
People want the absolute maximum power out of the smallest saw - bad for long life. EPA want them low on emmisions so they're running on the edge. Labour is cheap (and poor standards) overseas (no names...).
IMHO opinion this is true with all mainstream consumer products. It was considered a given that a 40 series landcruiser or pre 124 mercedes would get 350 km, do the bearings n rings, then get another 350 km, keep repeating till you die or crash it. Now people are impressed if a car gets 200 km before it's totally gone, with 150 being the general acceptance of a dead car. But people want a new one before 50 now, so who cares right? (70 series 'cruiser being the soon to be discontinued exception)
These are just snippets I've picked up from listening to people for a while, and impressions I've got from pulling things apart all my life. But I'm sure there are heaps of blokes that'll have different opinions and more factual takes on it so don't take that rant too seriously!
