While I like to soft reset my Pocket PC now and then, I do so because of memory usage, not because of cell site registration.
Also, a soft reset on a Pocket PC is just the case of poking the stylus in the reset hole. On a mobile phone it is just the case of power cycle - off/on again. There's no need to send it in for a "reset" to fix this.
The only thing I can think is the rep didn't want to say "we actually know there's a problem with this specific model and we need to flash the firmware on the phone again", which is arguably harder for some to understand then simply saying "your phone needs a reset".