I dont recall anyone saying it *had* to. I see a lot of people saying they wish it hadn't.
When you slap a tag on something that says "d20", that's a brand association, which carries with it certain expectations by your customers.
As a rule, customers are pleased when a product meets their expectations. After all, their *expectations* are a big factor leading them to purchase it.
I also feel, as a game designer myself, that d20 games should meet a minimum standard to increase compatibility between product lines, because this increases value and flexibility for the consumer.
As a recent example, I had a customer tell me he preferred Spycraft's Martial Arts system to that presented in Vigilance, but otherwise enjoyed Vigilance. That's great!
However, since Vigilance, DNW, and M&M all use feats, and SAS doesnt, to me that means a consumer of one of those three games, say M&M, would get more value out of buying Vigilance or DNW than SAS.