I tend to disagree on the differences
The guard changes, it has to, those gloves dont offer much in the way of protection so head movement becomes a much bigger factor
Its harder to box on the inside as you are more likely to get drawn into a clinch which is why you tend to see more boxers opting for the out-side.
The stance changes, Boxers can be very heavy on their legs and the angle that the lead leg is at leaves them very vulnerable to low leg strikes. also the legs tend to be positioned further back which changes the balance of the fighter and allows them to avoid take downs easier.
Muay Thai striking changes also, body kicks (highest scoring technique in muay thai) arent used as much due to the chance of them being caught and subseqently taken down.
But I think NRNS is correct about a person finding their own rhythm, taking from different arts to find out what works for them.
I can see in the long term people training in one MMA gym, which covers the lot instead of cross training over different styles in different places.
Its not about how hard you hit, its about how hard you can get hit and keep moving forward