Correct, if you don't _need_ the power, then stick with the 8051.
8 bit uC are not going away, but there is a overlap-shift at the top end ( code size, pin count ), so for a project that you know needs more than 64K code, or extended peripherals, or 64+ pins, then the ARM's can now compete with 8 bit.That said, you cannot find a socketable ARM, nor anything under 32 pins (excluding smart cards). There are also no ARMs with 24 bit ADCs.....
In the industrial sector, 80C51 dominate, with companies like Infineon [new 866/886/888], AnalogDevices, BurrBrown, Philips all doing 80C51 devices, and all with long records of sourcing.
Philips are extending their LPC family, up to 64KFlash
- even though they also have ARMs 'down-to' 8KFlash.
In the ARM sector, there are now ARM9's showing with FLASH, and doubtless there will be some rationalise of the ARM7 devices...
-jg