adventureluck , electronic equipments in the past are usually made by reputable or brand-name manufacturers (like Sony, Philips, etc). They have strict QC, so generally all their products works even after many years of usage (just like my 15 year old Sega Game Gear!).
The trend for same reliability but more MB would only apply to brand-name manufacturers currently. Although i suspect they have done alot of research and accelerated ageing for their equipment to fail not long after the warranty ends (that's how they make you purchase a new equipment every year to make profits).
That simply explains why a 10 year old electronic equipment still works today even with rough usage, but a 1-2year old equipment keeps making its way back to the service centre.
These things (i assume you are referring to the clones) are mass produced in China. In general, you pay for what you get. If you pay a very small price for it, you can't really expect much out of it. If they give better reliability, better functions, better everything than brand-name players at a fraction of the price, then those big companies would go bankrupt.