Different cords are created to different variances. Cheap cords can be very loose and easy to have bad connections. I am not a fan of the microUSB connector at all and think the miniUSB connector had a much better fit. However, it is what it is and I haven't had any major issues myself and I am guessing it would be possible for the connectors to get loose, but I think it's a combination of both.
My car charger is very loose, it was a $2 cord from china off ebay. My kindle charging cord, which is also microUSB, works fantastic. I love one thing about microUSB and that is that has become very universal.
As for your 2nd question... no idea. Never tried or researched. However, it looks like yes you can. I knew HC tablets supported keyboards, wasn't sure about GB.