Quote Originally Posted by Ядерное лицо
It's not that English-speakers can't say the -kv- sound, just that it's very unusual, so at some point in history, the pronunciation of Maskva was changed in our language to suit our ways of pronunciation.
Also, it's been changing in Russian over time as well, so "Moscow" may well be a very close transcription of some earlier pronunciation. An 'o' surely was there at some point: московский, Московия. Consider also a similar pair "церква"/"церковь".