Every full node checks the validity of the coinbase transaction. SPV nodes currently don't, but they could if we switch to using Merkle sum trees.
The power that miners have over the network is strictly limited to choosing the transaction ordering. Their attacks are limited to denial of service (mining empty blocks), double spending (chain reorgs), and censorship (selective rejection of transactions for political reasons).
But even this rests on the assumption that the folks running non-mining, verifying nodes are economically significant enough as a whole to resist miner fraud.
You're right, it is up to every full node to validate the blockchain, but to implement a change in the blockchain, you don't need the majority of users, or miners. You only need the majority of mining operators. Once they adopt a change, they can prevent everyone else from using Bitcoin until they comply with that change.
If the majority of mining operators (a very, very small minority of people) said "In order to spend Bitcoin, you must pay a 10% transaction fee (tax)." People would bitch and complain, but rather than letting go of their Bitcoin, they will comply with the new rules. If they decided to set Bitcoin on an inflationary tract, who's going to tell them differently? Uncle Joe, who's entire net worth is measured in Bitcoin? I don't think so. 90% are Uncle Joe, 10% will be cheering because their account balances will skyrocket!
Don't underestimate the general apathy of the people, it's a powerful weapon in the right hands.
Not to make this specific to the US, but that's where I'm at, so that's the example I'm going to use...
1866 - fungible gold certificates - fractional reserve
1913 - federal reserve bank given power to counterfeit our money
1933 - confiscation of gold - Dollar drops to 78 cents (vs 1932 prices)
1934 - Dollar drops to 58 cents
1971 - End of Gold Standard - Dollar worth 51 cents
1972 - Dollar drops to 35 cents
2014 - Dollar worth 1.5 cents
What happens when Bitcoin becomes THE currency and people devolve once again into apathy. Who's to stop the miners from destroying value just like the FED destroyed the value of the dollar by taking gold out of the equation and engaging in unlimited printing?
To coin Money, regulate the Value thereof, and of foreign Coin, and fix the Standard of Weights and Measures;
To provide for the Punishment of counterfeiting the Securities and current Coin of the United States;
Congress is supposed to be representative of the people, to work the people's will. The apathy of the people allowed Congress to do this to us. The apathy of the people allowed the wholesale counterfeiting of our money.
Apathy happens, it's a fact of human existence. Bitcoin does not have any controls to prevent abuses against an apathetic people. Honestly, I don't know if there can be a 100% safety net against apathy, but making collusion between mining operators more difficult would likely be a step in the right direction. I think I have a solution that would work on a new coin, but would be horrible at this stage of Bitcoin's development.