when it is decided by only a few guys that the official client only accepts transaction with a certain transaction fee and there is no "revolt" by users, miners cant do anything about it.
WRONG:
If more than 50% of miners are pissed enough that Millions of BTC get shifted around but nearly no fees are being paid, they can as I said 51%-attack the network and force fees as they wish. If the official client doesn't do what they want to, that's the official client's problem.
The Eligius pool for example ONLY includes transactions that follow a certain fee structure and also offers a modified Bitcoin client that automatically pays them (cheaper than the current fees by the way, but for every transaction). There's not much to loose currently for pools, transaction fees are anyways only 0.1-0.2% of a block reward...
I doubt however that the fee structure you propose will be adopted.
Including free transactions comes at a cost: Storage space. Every kB of transactions gets stored on every Bitcoin node all over the world + transferred + verified... a huge waste of ressources that is leeched by people doing transactions for free. The only thing saving them right now is that pools are operated by idealists rather than economists, at least to a certain degree. This won't be the case all the time.