If BT is off it comes on if you start a program that uses it. So, there should be no support calls from those users because they had BT turned off. The problem is things like BT keyboards where you need to turn BT on first.
There are a couple of valid problems with leaving BT on permanently:
- As far as I have been able to tell, in an unscientific way, leaving it on seems to drain the battery slightly more. Not much, but measurable.
- Some users will want to keep the BT visible as default, and just switch BT off when not using it. If BT were permanently on then it would be visible all the time, which is not always what you want, and you would have to go in and reconfigure it whenever you wanted to receive a file, for example. Much much easier to just turn it on and off, it it wasn't for the fact that the current BT icon disappears.

This is one of those cases where the designers tried to be too smart for their own good.