If you use 1k units per day, but only have one customer, the one that buys ten of those units each day, and he's the only one who wants ISP capability ... you certainly wouldn't use it in production ... then you need only one ISP adapter, or maybe a half-dozen. So, instead of spending $$$ on building a fancy feature into the chip, you spend it on the half-dozen or fewer adapters that are needed. You use that adapter with an industry standard host interface physically but not necessarily logically identical to JTAG, or IIC, or whatever.

Anyway ... this is a dead horse ...

RE