It is hardcoded to send the client a power list of 3575737816, 1765014394, 1732896497, and 1013339550. Cookie to the first person to tell me what those numbers mean*.
Granted, this is just a rough educated guess, but I'm guessing something to do with the individual powers' ID numbers within the client's power structured (Struct) database to look up and identify these powers' data from within the client-side's database so it knows what visual UI image to display in the tray, as well as which visual effects, sounds, and animations it should be referencing and pulling up to be played when the power is called...
Basically, the power information itself (its visual aspect at least, not its functionality) is likely all stored inside the struct database on the client's end, where each power is stored as a series of variables for all the needed client information(the visual aspects), and each power is assigned an ID number so the server can call the information up as needed without having to send excessive amounts of information to the client, since the client can just reference it locally without worrying about network latency.
It's possible, though I'm not entirely certain, that a portion of the ID number might actually reference specific variables within a specific power's struct information, allowing a single line like 3575737816 to tell the client that the power struct that needs to be pulled up is Flight pool's variation of Fly, and the client needs to play specific effects and animations according to the numbers in that line. So like (bare with me, rough number generalizations) 35 might be the first few digits to indicate that it needs to pull up the struct data for Fly, 75 might call up the specific animation state to be played, and 73 might be referencing the visual FX that needs to be rendered, and 78 could be telling it which sounds need to be played, and 16 could be referencing the specific power icon to be displayed in the tray and buff sub-display (not sure what it's called, the visual buff indicators that sit under the health/endurance bar).
I'm honestly a little iffy on this last part though, and I could be completely wrong about it, because it would become really cumbersome to be programming all the power references like this. It would probably require a massive spreadsheet just to keep the references all straight, but at the same time, it'd probably be a lot more efficient for the server to send and receive that single line of numbers to update all the client's information and have them pull it up locally than having to directly reference every effect, animation, sound, exc. separately to sync all the clients together to display the same thing... Of course, it could just have all those variables factored into the struct by default, and it's just pulling up all the information at once from the database in order to render and display the power being used, and the number itself is just a sequentially assigned ID number based on when the programmer actually made the power...
Again though, just a rough couple of guesses based off what I've learned in building my own games... I have enough experience in programming to say that that's what I would think to consider for designing the system (at a glance at least, in terms of actually building it though, I'd probably be doing it wrong and my brain would probably explode trying to straighten it out...), but I'm mostly an artist and not a programmer, so I could be thinking about this all wrong...