I would strongly argue there. ARM is not the only real answer, even among portable makers. The Intel Atom, VIA Nano both make solid x86-capable portable CPU's which are making inroads. New MIPS CPU's are arriving that put the ARM in for a run for it's money. Even the ancient 68k with ColdFire is starting to bring some excitement back to the field. ARM might be 60% of the market, but that is not the "only real answer" any more than m68k was in the mid 1980's, where it was in the top half and Intel was the underdog.
Last I saw, ARM was closer to 70%, but even at 60% it makes it a no brainer to port to ARM ATPIT. If MIPS or any other CPU gets 40% or better of the portable market, I'll be happy to see a port to that as well. Right now, it would be rather stupid to place any significant developer time on anything other then ARM. No one can afford another PPC like fiasco.
Dammy