Thanks, this makes sense. So after all it's a coding convention.
By setting the ROM start at $F000 (or $F800 for 2K) then those vectors end up where people expect them to be even though the 6507 treats $1FFA, $3FFA, .., and $FFFA as the same address.
This brings to my mind that I made an error with some code I wrote to relocate roms to phisical 13 bits addresses (trying to save some instructions to make z26 run at acceptable speed on the 3ds); I relocated 2k roms to 0x1000, just like 4k roms, but the correct position should be 0x1800 to have the interrupt vector(s) at the right position.
Strange thing is that the relocated roms work fine on the emulator (using javatari), but probably it's because the emulator, with 2k roms, ignores bit 13 of the addresses (just like happens with phisical 2k cartridges)