Apple didn't abandon, they provided an upgrade path.
First, they included "Classic" running within OS X for OS 9 applications. This environment sometimes ran OS 9 programs even faster than booting straight into OS 9 on the same hardware.
Second, they provided dual-booting into OS 9 and OS X for those rare programs that just wouldn't run under Classic.
Third, a couple years prior to OS X, Apple released an API that contained about 95% of the system calls normally used in OS 9 applications, requiring little modification to most programs to this API. OS 9 programs conforming to this Carbon API could run on OS X natively.
Fourth, for the transition to Intel, Apple built in a seamless emulator for PPC applications. You don't even know it's running unless you check. For those people using XCode, compiling your program to a universal binary (PPC and Intel) is simply a checkbox.
I wouldn't call that abandoning users.
I specifically mentioned Apple abandoning the Apple II users, but like most of my points it was either over your head or before your time.