Pretty much the only credit I'll give to Amazon is that they give the option to get plaintext emails. Doesn't mask the larger problems, but still a nice thing I wish was the norm.
Mind-bogglingly stupid and annoying.
Amazon's refusal to do so means you can't search your E-mail history for purchases (at tax time, for example). Or for warranty info or service. You may not know where you bought a particular item. Or which Amazon account you might have used.
If everyone followed Amazon's anti-customer example, you'd have to log into every E-commerce site you ever bought something from and search your order history... year by year... to find something. Unacceptable BS.