Why does every third party control set rewrite the basics of ASP.Net?

Question

Of the control sets I've seen for ASP.Net they all exhibit a strange property. They rewrite everything in the ASP.Net control set. For instance both DevExpress and Telerik have their own Panel, Label, and UpdatePanel controls among others.

Why do vendors do this? Is it just to create a form of lock in or is it actually necessary?

Answer 1

How is this rewriting the basics? They simply provide their versions of the ASP.NET controls (often derived from the ASP.NET controls). Their versions provide a better design-time experience, better features, or both.

That's exactly what they should be doing, and you and I should be deciding whether the additional features are worth the money.