I think that the thing with the 708A is that the quality is very variable and not all-around bad.
Lots of people (including me) have one that hums along perfectly with zero problems. Many other people have 708A's that choke and die (including me, last January.)
I think it's more of a question of the quality control on the production lines as opposed to the design of the product.
The PX-4012TA was made in Japan. The 708A was made in China. Clearly, they are on different production lines.