It's an issue because the GPL is viral, and AJAX libraries are like any other DLL in practice. You can't link with DLLs that are GPL without requiring your own

It's an issue because the GPL is viral, and AJAX libraries are like any other DLL in practice. You can't link with DLLs that are GPL without requiring your own program to be GPL too -- that's why the LGPL was invented. The GPL license would effectively require your own app's javascript to be placed under GPL too.