There are several HD channels that DIRECTV offers than have little to no HD content and no major sporting events to support their addition. If major sporting events were a concern, you would think they would have popped for the NBC/Universal channels for the Olympics.
I remain convinced that you're mistaken about DIRECTV's "major" motivation for adding the channels.
You're ignoring the fact that no other "major" sporting event can compare to the audience for the World Cup. The global TV audience for the World Cup dwarfs everything else, including the Olympics. It might not register as much for American audiences, but definitely does for Univision's viewers. And Univision's ratings for the World Cup are roughly triple those for ESPN and ABC's World Cup broadcasts.
The Olympics is a poor comparison because the events were split between multiple channels, with most of the audience watching on NBC and only one channel showing live Olympic events (MSNBC) was not in HD on Directv.
For Univision's viewers, the World Cup is appointment viewing and getting the event in HD would indeed be a major motivation for their audience. This is the same reason why HDTV sales every year peak during the week of the Super Bowl. At the very least, Directv should add Univision HD just to avoid a spate of cancellations during the World Cup. Failing to add any of the other missing HD channels won't have nearly as detrimental an effect on Directv's subscriber retention, as failing to add Univision HD in time for the World Cup would have.
Unlike other cable channels, sports is more of a make or break offering than any other programming. USA is the highest rated cable network, but dropping that network or not offering it in HD would not induce nearly as many cancellations as ESPN or the local RSN would. This is why ESPN's carriage fee is more than 6X greater than USA, despite USA having an average audience more than twice as big. It's also why the local RSNs' carriage fees are about twice as high as any of the national cable channels, except ESPN.