The 767-200 primarily flies between New York/JFK and both San Francisco and LAX. These prime business routes have long seen American as one of the two major players, but United's launch of p.s. service on those routes helped convince passengers to look toward United for a better experience. By all accounts, United's p.s. efforts have been a success, but I have to wonder if some of those gains they've made are now in jeopardy.
JFK-LAX/SFO are heavily traveled business routes, and the people on those planes have probably been drooling over the thought of onboard internet for a long time. For some people, spending 5 to 6 hours cut off from the rest of the world sounds enticing, but for many, it's a burden. American can now connect you for a mere $12.95 per flight and United . . . can't.
It will be interesting to see if there is any share shift on these flights in the near future as United no doubt scrambles to find something to compete (though I don't recall hearing about any plans from them for years). While this is likely going to be an important onboard amenity systemwide, on these heavily-traveled business routes, it should be an even bigger deal.