Well, as a DM I see it in some ways as a defence against bad role playing. If the PC could get followers without spending a feat, then I'd inevitably have someone asking why they didn't have followers and now I don't have to say 'Because you haven't earned them', I can say 'Because you haven't spent a feat'. On the other hand, if someone did through good RP earn the equivalent of followers, then I wouldn't mind letting him treat them more or less like followers and cohorts, but I'd give the player with the leadership feat a significant advantage in controlling these followers over the one without it.
In a former campaign, all the PC's ended up with retainers, henchmen, followers, cohorts, and hirelings enough to run a small country (which in many cases was exactly what they were doing). The difference between them is basically only how much the DM is willing to put up with before he takes them away, and how willing they are to risk life and limb on your behalf. Hirelings and followers may both be loyal to you if you treat them well, but only followers are going to go above and beyond the call of duty - ei break you out of prison, follow you to the bitter end, go with you into exile, help you in a rebellion against the King ect. Of course, even followers are only going to do this if you have given them reason to respect you.
If you haven't taken the feat, then I'm going to treat your followers like followers only if you've been extraordinary in your RP, but if you have taken the feat then I'm going to give you the benifit of the doubt.
cedric: So you let a player talk his way through situations even if his character has 3 CHR? I never let a player just say, "I try to be diplomatic so he'll give us a lift across the river" and roll a dice, but on the other hand, once a player plays out what he wants, his character still has to make the diplomacy check (with a circumstance bonus or penalty depending on how well the player performed).
And yes, I've observed that in real life only people with high charismas are capable of successfully intimidating people. I don't care how big and scary you are, swagger badly, and you just infuriate people. Scaring people and intimidating them into doing what you want or entirely different things. On the other hand, I've seen children bully and intimidate people quite successfully.
That is not to say however that the intimidate mechanics don't need fixing, just that they aren't broken in the way that people usually complain about.