<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by rbAA:
Apparently, Site59 uses S class fares, whereas on AAvacations.com, they use L. </font>
You're partially right. The vast majority of AAVacations bookings are in S class as well. L, S and V class bookings on AAVacations are not upgradable with miles (and I assume VIPxx). You must pay extra to get into at least N class first. (I've been there, done that.) All classes of AA flights from Site59 and AAVacations are eligible for domestic e-upgrades per the normal rules.