States charging tax for digital downloads

I am always interested by e-commerce. Here is a list of states charging tax on digital downloads:

1. Alabama
2. Arizona
3. Colorado
4. District of Columbia
5. Connecticut
6. Hawaii
7. Indiana
8. Kentucky
9. Louisiana
10. Maine
11. Mississippi
12. Nebraska
13. New Jersey (BOO!)
14. New Mexico
15. North Carolina
16. South Dakota
17. Rhode Island
18. Tennessee
19. Texas
20. Utah
21. Washington
22. Wisconsin
23. Wyoming

Source: http://taxes.about.com/od/statetaxes/a/sales-tax-for-digital-downloads.htm

So far on-line stores only have to charge tax in states where they have a physical presence. This is why most of us can shop tax-free at Amazon.