Seems like a no brainer for FFG to make one of these at this point, was probably a coin flip between the Avenger and Defender at the time for which they'd put out first. I might get one of the rounded ones to use as a named Advanced pilot for when the Raider comes if the Avenger isn't in the next wave.
Semi-necro, but...
I don't think that's it. The Avenger hasn't shown up anywhere outside of the X-Wing and TIE Fighter games. The Defender has been in books, there was a MicroMachines Action Fleet model, and there was even a LEGO set made of the Defender (I know - I have one). And both the Defender and the Phantom (which actually has less screen time than the Avenger - by one game) were featured in Empire at War - Forces of Corruption .
I think the Defender gets so much attention because everything about it is completely nuts, especially if you're used to the depiction of the ship in TIE Fighter . Heavily-armed, heavily-armored, fast, and maneuverable. The Avenger is no slouch, but it's basically the red headed step-child of the TIE family: Too advanced to be commonly seen in bad guy goon squads (or good guy "commoner" squads) like the Fighter, Bomber, and Interceptor, but not as gonzo as the Defender for when you want to kit out your big bad (or elite good guys) with a ship so powerful (and expensive) that no other starfighter in the universe can hold a candle to it.