So what. We see Mos Eisley but we don't see a battle going on there. We don't see a battle going on in Kamino or Yavin IV or Dagobah for that matter. No battles occured on Tatooine (unless you count the skirmish over Carkoon, which is conspiciously absent from both games) and we got three of them in the games (four when you count the new space battle, which might refer to the "battle" between the Tantive IV and the Star Destroyer, so you could argue it might be "canon")! Just because there wasn't a full scale battle (Bespin was a skirmish between individuals and a handful of troopers as well) on that planet in the movie doesn't mean we can't imagine one in the game. The majority of the battles we see in SWBF1/2 never happened anyway. They're all made-up. So it's not an issue of being true to the movies, only that these all exist in Star Wars, so they're fair game. Alderaan was featured in ROTS for the first time in a SW movie (the surface), as were these other planets, though at least we'd known about Alderaan before ROTS. If anything it had more of a "right" to be included than Mygeeto or Felucia!
We see as much of Mygeeto and Felucia as we see of Alderaan, so I don't think it's a valid argument to say that because of this Alderaan is automatically out.
When the DVD comes out you can see Alderaan's surface at the end of the movie where it shows Bail and Mrs. Organa holding baby Leia in that city. We see as little of this planet as we do those others, so we can make it into a battle just as easily.
Polis Massa was seen much more, you're right, but we mostly see that robot maternity ward. If there is going to be a battle on that planet, it's not going to be inside that tiny waiting room or the adjoining operating room. It's going to be on the surface, which we only see for a few seconds. It looks like the moon with lots of asteroid debris nearby.
Anyway, I don't see any logical argument why Alderaan couldn't have been included (many more logical reasons why it could have been put in), they simply chose not to put it in.