Mb = megabits
1 byte = 8-bit
(As a historical side note, there was even a weird transitional period where a “1.44 MB 3.5 floppy” held 1.44 * 1000 * 1024 bytes, or what everyone at the time would have called 1440 kilobytes.)
Personally I think it’s unfortunate that standards bodies and even courts have sided with the disk manufacturers. I also find the SI binary prefixes utterly revolting on an aesthetic level, so I’d much rather join whatever parts of the tech industry are still holding out.
Perhaps HNers know better, but among lay people, pretty much no one talks about megabits. For example, people know that an MP3 is about 5MB. They know that they can email attachments up to 20MB (or sometimes 10). But I've literally never heard a lay person talk about bits, or bits per second.
And the fact that ISP's transfer caps are denominated in bytes makes things all the more confusing.