While it maybe true that samsung is doing better in sales than Motorola I doubt the bootloader has anything to do with it. Most people who buy android phones have no clue what a bootloader is, what rooting is, or what a rom is. They just want a phone that looks good, and gives them a good experience. The fact that Samsung has better camera will account for far more sales than the bootloader.
I used to root and rom. I installed more roms than you can shake a stick at on my incredible. Had fun but I have been there and done that. The thrill is gone. All roms fixed something and broke something and none including cyanogenmod were as stable as stock. My bionic is not rooted, won't be rooted nor will I install roms. I don't care about the bootloader. I just want to call my wife and my mom, send email, discover the names of birds with ibird pro and control my telescope with Skysafari pro. Those thrills are better than installing a custom rom and wake up late because the phone froze and my alarm didn't go off.