Rumour has it (not sure if this was ever confirmed) that one of the big reasons the second Xbox was called the Xbox 360 was to avoid unfavourable number comparisons with Sony. The Xbox launched vs the PS2, which meant the "Xbox 2" would compete against the PS3. As 3 is bigger than 2, it would make the second Xbox look bad. Hence, Xbox 360. Both have a 3, no number issues. For what it's worth, Robbie Bach (former Chief Xbox Officer) is on the record as saying one of the potential names for the second Xbox was just "Xbox 3" to catch up the PS3.

While officially the meaning of the "Xbox One" name was something about it being an all-in-one entertainment system, I would put money on it being chosen as some kind of subliminal naming scheme as it sounds like "Xbox Won".