Actually, I think more hardware is cross-compatible between the VIC and 64 than between the 64 and Plus/4. The 1541 will work, but I think you were supposed to get the (faster? just different?) 1551 for the C16 and Plus/4.
They designed the C64 partly to use the same hardware add-ons (datasette, disk drive etc) as the Vic20. Sadly this means it was also saddled with the slowness of the serial connection for the 1541 where they could have made something newer and quicker.
How was it - the VIA serial routines were buggy when the VIC-20 project was to be released, so they had to stick with a slower version, and later when the C64 arrived, the routines (now applied to CIA) were fixed, but could not be incorporated to break backward compatibility?
They designed the 1541 for the C64. The 1540 that was the original Vic20 drive is faster than the 1541. Just as swithing the 1541 to "vic-20 speed" with the "UI-" command. So instead of making the disc access faster, they made it slower on the c64...
/Anders
PRG Starter - a VICE helper / Vic Software (Boray Gammon, SD2IEC music player, Vic Disk Menu, Tribbles, Mega Omega, How Many 8K etc.)
.. due to more complex timing (VIC-II) I believe. It is true that a better serial protocol/routines could have been used to get faster access, but it would break compatibility. Remember that most C64 disk speeders close the screen in order to get as fast transfer as possible.