speaking from a Travel Agent's point of view and experience with this matter... a ticket is a ticket whether it's electronic or paper, the allocation of exit-row seats is usually governed by the amount of the ticket and the level at which one's Frequent-Flyer account has reached (i/e Advantage Gold or higher, Delta Medallion or higher etc..) as well as the rules a particular Airline has placed on the assigning of these seats whether it be allowed in advance or strictly at the airport. Sounds cut and dry right? WRONG!
Every carrier bends their own rules (.. some to the point of breaking) so, IMHO, it boils down to A.) the competence level and/or disposition of the representative you conversed with - Res and/or Travel Agents included- and B.) one's ability to be persistent and not accept an unreasonable answer.
The requlations that the FAA (for U.S.) put forth mandate that those seated at exit rows be of a certain age group, physical ability and willingness to take on some responsibility should need arise. None of which can effectively be determined IN ADVANCE.
The bottom line of this narrative being, getting an exit row seat is up to God and even he/she has probably been given a false answer.