The ARM core is of course designed by ARM, not Philips/NXP. My understanding is that a significant number of the peripherals are also ARM designs, and that ARM supply the design to the silicon manufacturers at the transistor/mask level, and expect the fab to use a specific process, e.g. 130nm, 90 nm etc. The silicon manufacturer does not get an opportunity to fiddle with the core because he is not supplied with a synthesisable design source. This means that the ARM devices all tend to have predictable behaviour and performance.

Philips/NXP have certainly added an impressive FLASH interface to the ARM7 which allows the core to run at full speed.