Philips has 10,000 minimum erase/program cycles for each byte, not 1000. So that is not much difference because usually your development gets over withing max. 3000-5000 erase/writes.
I meant difference in terms of SFRs and their addresses.
I think the MAIN difference is the Atmel part can erase one byte at a time in the flash thus making it very powerful. In case of Philips, you must erase an entire sector.
So, you can replace a Philips part with Atmel but NOT vice versa.