Nick Jr. vs. PBSkids
.com vs. .org
Follow the money. :)
Nick Jr. is a commercial venture. That's why the pop-ups are all over the place. You know this is paying off at the toy store, at the grocery store, at the drug store -- anywhere tie-in products are available. Maybe not with your kids, but with thousands of kids across the country. The marketing blitz begins at a very tender age.
PBSkids is, well, PBS. It's non-commercial. Congress has just restored PBS's Federal funding, after attempting to cut it. Apparently, the "call your Congresscritter" campaign worked. Every time you don't see a pop-up on your daughter's computer, that's why. That, and all the millions of people who give money to support PBS every year.