Speak for yourself. As a code-savvy designer, who splits everyday designing on paper, in Photoshop/Illustrator and in the browser, I don’t think I can overstate how woefully our professional tools for web design have actually kept up with web design.
photoshop doesnt even have rounded borders
Sure it does—vector shapes + Stroke Layer Styles work great. Do you mean something else?
Every time somebody complains how Photoshop doesn't have rounded corners, they mean it doesn't have dynamic rounded corners. You can't change the roundedness in any remotely easy way after you draw the shape, and changing the dimensions of the shape distorts the corners.
They're just a huge pain to work with, when they need to be trivially easy for doing web design.
Any capabilities along those lines in a web app would probably be a bit more limited than desktop apps, but that doesn't mean that useful tools for vector and bitmap manipulation can't be made at all. However the case could be made to use desktop apps for what they're good for, and web layout apps can then reference files created with the desktop apps.
I agree there is a need, but I think that need is exaggerated, writing html / css is pretty easy, its not fun but its generally nothing compared to the overall work, half the time you still have to do it manually anyway since it has to fit into frameworks etc.
I want something that lets me focus on the design aspect, it should have nice snap to grid features, ability to inspect and edit css, but it should also have a vector drawing tools, image manipulations. The current set of design tools have terrible support for most common web functionality, photoshop doesnt even have rounded borders, illustrator / fireworks / sketch / pixelmator all almost entirely ignore things that are important for designing for the web. However web based editors almost all lack any graphical and vector capabilities whatsoever.
I started on this and gave up a while ago, http://upmock.com/ and wrote about it http://arandomurl.com/2012/10/15/upmock-is-dead.html. Currently the most promising so far has been SVG Edit, however it doesnt seem particularly active nor has there been a focus on producing web designs