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.