Yep, the 80%-90% level is pretty easily met by doing those along with using the native controls (buttons, links, etc.) properly. When your designers hand you a custom interactive widget, you can add a good chunk (50%-100% extra effort) to your estimate to make it accessible.
I struggle getting designers to consider how a thing is supposed to work without a mouse for instance.
a lot of designers I've worked with don't come from a web development background - they typically come from print design. They know how to make things look good, but when it comes to user interaction, or web specific functionality they don't know that they have to deal with much, much more than what you can see in the first instance.
You can't just design something and have it look good, you need to consider what happens in x, y, z scenario, and if you don't have experience, you don't even know those things even exist.
I struggle getting designers to consider how a thing is supposed to work without a mouse for instance.