It's not just cord-cutting, however, this changes Sesame Street's relationship with PBS, and over-the-air broadcast service. The group Sesame Street needs to reach the most is not cord-cutters, it's people without an Internet connection. Low income and low literacy families are what Sesame Street was created to reach, that's why it's a show designed to appeal to both kids and adults. Certainly with a show like Sesame Street having the newest episodes is not necessarily critical (though they have done some good topical pieces in the past, the episode where a Hurricane hits Sesame Street comes to mind), so it's not a major issue in this case.
Needless to say I was happy to see that there would continue to be some relationship with PBS, and I can't emphasize enough how important I find over-the-air public programming (both TV and radio).
EDIT: To be clear, I do not necessarily think this is a bad deal. I think the STW produces great content and anything that helps them continue to produce quality non-commercial content is great. I just hope that content continues to be available for free on over-the-air broadcasts in the long term.