This requirement negatively affects a rounding error of consumers that will probably be able to circumvent the restriction anyway.
Googles forcing G+ & Gmail apps onto a vast majority of users that don't use those platforms is arguably a bigger consumer problem. But nobody cares and rightfully so. The impact is minimal in both cases.
Beyond the negative effect there's a tangible security gain here that is probably a bigger deal for many more customers then are inconvenienced by the locked bootloader.
Microsoft is not the EFF and has no mandate to be pro-open source. Google's failure to release the Android development branch, roadmap, the honeycomb delay and their compatibility tests aren't anti-open source?