The batteries have held up fine over the five years I've had the pair, but I dread the day that they go.
Yes, before that time there were some excellent headphones about but they were much bigger and bulkier, for example, Sennheiser's professional series—also they were much more expensive.
Clearly, there was an impetitive for Sony to develop them, as it needed a range of high quality headphones that had to be in keeping (both in style and performance) with its extremely popular miniaturized Walkman players. (In the 1980s Sony Walkman players were all the rage, they'd taken the world by storm.)
Essentially, by the time you'd bought yours Sony had long done most of its R&D. Little doubt the manufacturing infrastructure to make headphones was still in place from the 1980s.
Incidentally, when I was in Japan in the 1980s, I bought four Sony Walkmans in one hit. They were excellent machines.