...I hate to say it but those results wouldn't lead me to that conclusion. They are subjunctive results, not absolute. You're comparing audio formats at low bitrate to others at low bitrate. They are only being compared to each other and cannot prove that "the quality at 48 kbps is acceptable" as there was no high bitrate option for people to choose. At the end of the day, music encoded at that bitrate can't compare to music at 128 or 192kbps or above, and such low bitrates as 48 were really only intended for speech recordings.

I can agree that these files are probable "good enough for Internet streaming or portable use with cell phones" though, as you don't expect quality from those things (at least until we get even faster internet connections which can stream at high bitrates with no problems).