Arms generates rage from auto attacks, primarily (or talents). The shift at level cap is that you get “free” attacks through Overpower resets (since OP doesn’t cost rage), and Execute on Sudden Death procs (or you can talent Skullsplitter, which generates rage). The spec is about managing your rage spending to ensure you can always Mortal Strike on cooldown (or pool for Ignore Pain if a big hit is coming).
Fury is a generator spec, where basically everything you do builds rage, and your only spending options are Rampage (big DPS chain + Enrages you), and Ignore Pain (defensive spender). AAs also generate rage, but most of it will come from your abilities themselves, and it’s GCD-locked with Whirlwind as the filler when nothing else is available to use. The spec is about preventing rage capping while maximizing generation and Enrage uptime.
Protection is also primarily a generator spec, with most of your rage coming from Shield Slam (and Thunder Clap, with supplemental from AA), or cooldowns. You spend rage on Shield Block or Ignore Pain to mitigate, or Revenge as an offensive AoE dump (and Execute as a ST option at 20-0%).
Windfury ends up being a huge buff to Arms, since it procs white hits that generate much more rage. Since Fury’s AA buff it helps them more than it used to, but still nowhere near as much.