Originally Posted by
VegasGambler
It's not really uncommon to not charge a premium for better seating. On UA, flying to Hawaii, they have some lie-flat equipment and some non-lie-flat equipment. The same fares with the same rules apply to all of them. AS is the same -- I've never seen a fare with equipment limitations.
While you won't typically see equipment limitations, there are plenty of fares with flight number restrictions, and these typically involve a subfleet on a premium route, or to prevent routing at a lower fare for connecting travel using a premium route aircraft as part of the trip.