While it bugs me, I understand that from an ISP's point of view, it makes sense to use whatever plausible-ish unit will let you post the highest number, even if that unit is way less practical for thinking in (any download large enough to be affected by connection speed is going to be thought of by the person downloading in terms of bytes, not bits). Also, if an ISP doesn't do that, everyone else will, and they'll be the loser in a prisoner's dilemma. However, what really bugs me is when third parties (e.g. the Finish government) perpetuate the inferior standard, which arose as a marketing ploy, for no apparent reason other than maybe ignorance. It's bad enough that we still don't really use the metric system outside of science in the United States, and it's cost us a fair amount of money in incorrect conversions. However, with MBps and Mbps, most laypeople and possibly some Finish government officials don't even realize that there are two systems, one of which is almost an order of magnitude larger.
Measuring transmission speeds in bits is a well-established tradition, e.g., modem speeds have always been reported in "baud" (bits per second). On the contrary, it could be claimed that bytes are an arbitrary unit (despite being a ubiquitous convention), whereas a bit is the fundamental unit of information. That said, it would be more convenient if all speeds were reported in megabytes, and aside from throughput, latency and packet loss should arguably be advertised as well.
