First, this is a silly ad hominem criticism; their arguments have little to do with their Enso application. But either way, these humanized guys are in general on top of things, and their thoughts about interface design are usually quite insightful. Implementing good interfaces, and insightfully criticizing interfaces, are two very different skills.
Second, while I personally love Quicksilver, it has a significant learning curve. Enso's model is, for better or worse, rather simpler. And beyond that, experimentation is good. A direct clone of Quicksilver would be both out of place on windows, and also much less interesting to create than a new application, with its own ideas.
And, hey, what's with "a direct clone of Quicksilver would be out of place on Windows"? No it wouldn't. It would be more appropriate. Quicksilver on the Mac competes with a lot of well-thought-out workflow that already exists in the OS X interface. Quicksilver on Windows would add far more value. And the QS "search-and-act" idiom is universal.
Have you used Quicksilver? You should. It's pretty amazing.
Second, while I personally love Quicksilver, it has a significant learning curve. Enso's model is, for better or worse, rather simpler. And beyond that, experimentation is good. A direct clone of Quicksilver would be both out of place on windows, and also much less interesting to create than a new application, with its own ideas.
Third, what the hell is Launchy?