The customer is more important than the engineering, 
    as long as the engineering supports what the customer 
    is trying to do

That is, and always has been, pretty much the entire point of good engineering practices such as keeping one's markup as semantic as possible -- allowing us to deliver stuff more gooder and fastener to the customer.

I don't think anybody has ever been under the belief that customers really were gonna do a "View Source" on a web page and just marvel at your clean HTML.