Website Usability points

While testing i have come across many such incidents where ROI of website is very much high, client is building very high profile website but some basic usabilit issues are missing and they are not considering it well to incorporate. As DEV perspective it may right but as QA point of view and business point of view as well it marks high.

1. FAV icon
2. All elements having tooltip as and when necessary
3. W3C validation
4. No html, css, JS errors
5. clean and intuitive design layouts etc.
6. User friendly navigation
7. CSS and validation message
8. Basic flow and functionality like login, signup , header and footer
9. Of course device friendliness
10. and much more stay tuned.