Just like PNG output from Photoshop, soon HTML+CSS output from design applications will beat most humans, or at least be reasonably close so that this complaint doesn't apply any more. It's not very hard to do a lot better than the source code of this web site.
Will Google design their homepage with Muse? No, they want to hand optimize it. Will people design websites for small businesses that get accessed a handful of times per day with something like Muse, when its output gets better? Yes. It might not make nerd-sense, but for a lot of sites it does make business-sense to have an increased page size in return for saving a lot of design and development time. Think of it this way: of all the things a person designing a website for a small company might spend their time on, is reducing page size the most profit increasing activity?
Will Google design their homepage with Muse? No, they want to hand optimize it. Will people design websites for small businesses that get accessed a handful of times per day with something like Muse, when its output gets better? Yes. It might not make nerd-sense, but for a lot of sites it does make business-sense to have an increased page size in return for saving a lot of design and development time. Think of it this way: of all the things a person designing a website for a small company might spend their time on, is reducing page size the most profit increasing activity?