I've been reading about these and they're pretty prominent in the .NET world. Why aren't there any web frameworks that implement any of these patterns in Ruby, Python, or PHP? Is it because it only works with component-based frameworks, like ASP.NET? Or are they just slow to adopt it?
The thing to remember is that these are architectural patterns - not frameworks. Frameworks only "help" implement the pattern, but it's possible to implement the pattern using any technology, provided it contains the correct requirements for the pattern.
MVP is present in other languages. It's a pattern that works when using with Python with PyQt, for example.
MVVM, however, is really dependent on some features unique to WPF and Silverlight - most notably the data binding features that are rather unique in these technologies. Though it would be possible (potentially) to modify this for other languages and architectures, it has not been done at this point, to my knowledge.