Max texture size is a limit built into your graphics card. Only the most expensive cards (and some more reasonably priced nVidia ones) have 4096x4096.

"Detail Area" in the options is related to texture size, but is an internal Google Earth metric that uses many times the number with of video memory: 1024x1024x(4bytes)xN where N is pretty large. This is why you really need 128M+ of video memory to happily use 1024x1024.