My point is that most other companies are like that, and the difference is just the extent to which these parasitical "internet businesses" are coupled to their host.
They're not `keeping the money`, they're just not paying you stuff that's not covered by the contract, TOS etc.
It's not `without warning` by the same token; unless the warning they were expecting was to hear about other companies who play fast and loose with the rules getting caught first.
Amazon pays ~2 months after Affiliate fees are earned, so at any given time you may have 2 months of fees waiting to be paid. If today they decide that they're done with their affiliate relationship with you -- for good reason or for no reason -- they can (and do) close your account with no explanation, AND they keep those 2 months of fees you already earned legitimately with no recourse except your suing them (good luck with that).
It's a bit like being a commissioned salesperson, getting fired, and the company keeps all your pending commissions. Totally illegal in that context, but the Affiliate program is not an employer in that way. It still sucks just as much.
A lot of companies warn you if they think you're in violation of their TOS: internet providers, game companies, cell phone companies, on and on. I don't think it's unreasonable to use a 'strikes' system or provide an avenue for appeal.
But Amazon can. They also pay a few months in arrears, so one day you may wake up to a form email that says essentially, "adios, and I'm keeping the money". In fairness, I believe all affiliate programs are like that.