Yes this is kind of funny. My understanding is that Thomson and Richie deliberately left out non power-of-two word size support (which other languages had at the time because cpu manufacturers were adding a couple of bits at a time to new models (Get this years 14bit cpu, two more than last years' cpu!).

To make a more simple, more elegant, more portable language they decided to settle on power-of-two word lengths. This is similar to how Unix came about, leaving out the cruft and complexity from the over engineered Multics.