From the OS perspective, current WP7 phones actually have less hardware variation than iOS devices.
iOS currently supports two CPU/GPU hardware platforms (Cortex-A8/SGX535 in the 3GS/4/iPad, Cortex-A9/SGX543MP2 in the iPad2) and three resolutions (480x320, 960x640, 1024x768). iOS also used to support the ARM11/MBX-Lite platform in the Original/3G, but that was dropped about a year ago.
WP7 currently supports a single CPU/GPU SoC (the Qualcomm QSD8250) and a single resolution (800x480). WP7 also has RAM (256MB) and flash (8GB) minimums on WP7, so there isn't much variation there either. Even the new WP7 hardware platforms don't change things up much. Qualcomm is still the sole SoC supplier and the SoCs chosen are pretty much just higher performance, lower power consumption parts.
Not that there aren't some implementation differences in WP7 phones (JBOD microSD...), but performance is pretty consistent across WP7 devices.