"One thing that led me to believe the Atmel 89C52 might be hardwired is that the datasheet says "compatible with MCS-51 products" and I thought that since the MCS-51 is hardwired than maybe the 89C52 is." (my emphasis)

Paul,
the key word here is "compatible" - this is where Erik's view is important: things can be "compatible" from the external, user point-of-view without needing the same internal implementation!