When comparing the Intel 64 [1] and ARMv6[2] instruction sets that's a quite trivial assumption. The difference on the number of instructions implemented by those architecture reflects well the complexity gap between both.

Also, there are many other details that make targeting ARM much easier, for instance the bootloading process on ARM is more straightforward with no BIOS or EFI involved[3].

1: http://download.intel.com/products/processor/manual/325462.p...

2: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc....

3: http://www.keil.com/download/docs/52.asp