This was certainly not the case on PC's. You began to see advantages as early as 1G because that is when some memory had to be moved away from permanently mapped memory on 32-bit. You ended up with a less than 200MB high memory area which was difficult to use effectively and you had to pay the PAE overhead to get it. Best option was to run a non-PAE kernel and forget about that last bit of memory (or run a custom memory split, if you like compiling your own kernel).
2GB was more or less ok and 3GB was a bit of a sweet spot (but who has that?). 4GB brought the extra pain of having to deal with 32-bit devices and DMA32 memory, or you did the sane thing and just gave up on a few hundred MB again to avoid bounce buffers. To be fair, DMA32 plagues 64-bit Linux as well, but it should not be much of an issue on modern hardware anymore.
Anyway, Android uses a 1GB/3GB memory split, so 1GB is still an unfortunate amount of memory, and all current Android devices are 32-bit.