As a regular user of a minimig is a pic programmer needed?
Sorry to hijack the thread btw 
Say, when new cores for the minimig are released. Is it needed then?
Yes, when the new Firmware's are released (For the pic), without the Bootloader (Tiny), you would *NEED* a programmer to update the firmware.
Thats where the Bootloader comes in, it receives new firmware via RS232, and flashes the chip automatically.
And i think that is where the Original poster has lucked out.
Of course, the PIC replacement that has been announced, can be flashed via USB 1.1