The LCD logic is quite slow and thus work reasonably well in memory-mapped configurations with yesterdays chips.
What many do not appreciate is that if you use a faster chip, you need to change the hardware, not just the code. A LCD with the write clocked by !WR from the uC will only work if !WR is within the specs of the LCD. Thus, with fast uCs the LCD must be controlled by external logic or port pins (Pn=x). The saving grace here is that while the memory mapping is lost, this can often be accomplished by using a chip with internal memories freeing up P0 and P2 for port drive of the LCD.

So you find 'some code guaranteed to work' and find out it does not because it was written when 8 MHz was considered fast.

Erik