Not all tuxedos come with sleeve buttons.  A growing trend is for manufacturers to not include sleeve buttons on the tuxedo.  Some gentleman like the clean look of no buttons on the sleeves.  Other gentleman like the idea of only having 1 larger button on each sleeve.  Others prefer having either 3 or 4 smaller buttons on each sleeve.  Some gentleman may want to do something crazy and different with their buttons like use a different fabric or having monogrammed buttons on the sleeves.

 

No need to put a lot of thought into the sleeve buttons issue.  Sleeves can easily be updated/changed by a local tailor for a nominal fee.