I think you are over-simplifying the use of the conjunction. If I had a right to "dance and sing", you would claim that I can't simply dance without singing or sing without dancing?
No. Since you can do both - 'sing and dance' - doesn't necessarily mandate you MUST be doing them both at the same time. What if, however, you could not dance without singing? In the case of bearing arms, the ability to keep arms is a prerequisite to bearing them.
Considering them separate Rights implies the ridiculous notion that you could carry something you didn't have the acknowledged right to have in the first place!
IMHO, that's also why they used the unquestionable joining conjunction 'and' instead of the refining/exclusive conjunction OR.