Before the AIA (September 2012) the answer was simple, the inventor had to apply. Now an assignee or a company with an assignment clause in its employment contract can also apply. Is there a reason not to do so? No, but don’t get lazy. You will still need to file an inventor’s oath, and you will need to record the assignment or employment agreement (37 CFR 1.46(b)(1)) with the assignment clause before the issue fee is paid. If you don’t have these on hand when you file the application, you may be better off filing with inventor as applicant and follow the pre-AIA procedures.
Remember to record the assignment within 90 days of execution. Currently it is taking 30 days to get the reel/frame number sent to you by email, or a notice of non-recordation (if you made a mistake) so start early.
New Rule 1.46(b)(1) tells us:
(1) If the applicant is the assignee or a person to whom the inventor is under an obligation to assign the invention, documentary evidence of ownership (e.g., assignment for an assignee, employment agreement for a person to whom the inventor is under an obligation to assign the invention) should be recorded as provided for in part 3 of this chapter no later than the date the issue fee is paid in the application.