I think there is a potential for higher fidelity, sure. But memory and bandwidth constraints are also present on the 360 and even more so on the PS3 that I believe put a cap on how much of that potential could be realized. Sony needed to put BR in the PS3 to promote BR as a movie format. Looking just at the benefits that have been realized in games in no way justifies the costs of its inclusion.
If it had been possible for the PS3 to launch a year or 2 later with more memory, a faster drive, and other tweaks to allow the system to better leverage the additional storage in a way that made sense for developers and publishers I think it would be a completely different story. It wasn't possible, though, unfortunately.
And the CD->DVD transition for PC games took a really long time past when DVD-ROMS first became available. This despite the constant march of PC hardware advances.