Hrm. I'll first say that simply macroing HS will result in damage a good deal lower than manually spamming HS, or keybinding it to mousewheel and spinning. You'll miss a fair number of white swings if you do simply macro it, since there are often long enough times when you aren't hitting other buttons. I often raid with another fury warrior, and I can wind up Heroic Striking as much as 20% more than him, probably due to more thorough button pushing due to a manual "/cast !Heroic Strike" macro on a separate button.

Second, while Execute's damage does drop down below a Slam proc pretty easily in ICC gear, it's worth having on the bar, if only as GCD filler for when slam doesn't light up and you don't have to refresh sunder. For me on a recent 25h Saurfang, it was 1.5% of damage or so, but that's still 1.5% more damage than I would have done if I'd left the button off the bar.

I guess I don't care how many buttons an average Fury warrior will have to push, but how many a great Fury warrior should be pushing. Granted, it isn't many more, but it takes more than three to truly excel.