20? There are a handful of major faction storylines, and depending on your choices you can get different branches even in the same storyline. For most players they'll be satisfied seeing the ending for each faction, that boils down to about maybe 5-6 of them.

If you play enough times you'll notice that the ending cutscene actually consists of several cutscenes spliced together. Which ones appear depends on your decisions during the game. Perhaps Rastix meant 20 unique combinations of these cutscenes. But most of them are just different variations on the same ending. For example if you play MSF there might be 2-3 ending cutscene combinations. Most players will likely just count it as "the MSF ending" and not quibble over the variants. If you want to be fussy and get technical then yes each of them are separate unique endings... but most people will not bother with minor differences in what is essentially endings for one particular faction.