Users not closing their tags? It's OK, we'll complicate the parser to accommodate them. Users want to interact with what should be static documents? No problem, we'll throw a scripting language in there. Users want to interact with hardware peripherals? OK, we'll just expose that.
The real tragedy is how much of systems research has died at the hands of this crappy sentiment of Good Enough that pervades the Web. Literally everything the Web touches gets infected with Good Enough.