Spark plugs only last 7 or so years because the spark erodes the electrodes.
A correctly running engine takes hundreds of thousands of miles to wear things like valves and injectors. The system does run more pressure than your typical EFI system but current manufacturing processes might make that a non-issue.
A correctly running engine takes hundreds of thousands of miles to wear things like valves and injectors.
I disagree about the injectors. I'm particularly anal about mine, and on every 75k-100k mile engine I have noticed a considerable improvement in engine operation (idle smoothness, etc.) when I send my injectors out for a cleaning.
In reality, injectors don't become enough of a "problem" on most people's cars to service every 75k miles, but they certainly do not perform as new.
Having said that, I suspect that direct injectors are a completely different animal and my experience with "regular" injectors is irrelevant when it comes to direct injectors. Maybe better, maybe worse. I hope/think they will be better, but time will tell.