With what right do you consider yourself in the position to judge their intention?This is easier with some kind of sites than with others. If it's a company site trying to sell a product or a service, then obviously the intention is to... sell you the product or service. If the "design" doesn't push that intention or gets in the way of you learning about the product and why you want to buy it, then they've failed.
With personal sites and blogs it's harder to judge, and I'd agree with you. But I think in those places design (at least in the sense that the author is talking about) is less important. Someone's personal site might in part be a sandbox or playground to try out new HTML5 or CSS techniques.
Everyone's opinion is subjective. Claiming that that somehow invalidates the argument is disingenuous. Like everything, it's a continuum -- some things are easier to "objectively" judge, others are not and are more a matter of taste and experimentation.