I just scanned this thread, so I'll apologize in advance if this bit of brilliance is a duplicate...
My guess is that those who "cheap out" on their trailer, do so because they don't haul their boats far. I know folks in Tobermory (Ontario) that have never moved their boat more than a half kilometer at a stretch. Backyard to ramp. Ramp to backyard. Indeed, that is mostly me too... And I can damn near hit the ramp with a good throw from my front yard. For this use, I could use a shop dolly or a wheelbarrow to launch with, if they were big enough.
However, I occasionally tow much longer distances though, so while my trailer is older, all of the stuff on it has been replaced at one time or another... axle, springs, hubs etc.