If MacUpdate isn't recognizing popular Mac apps (they show up as "grey" and disabled), it's because your MacUpdate Desktop prefs file has been corrupted. It's really easy to fix.
Simply quit MacUpdate Desktop completely using the "gear icon" in the menu item. Then relaunch MacUpdate Desktop while holding both the Command + Option (⌘⌥) keys.
Once Desktop is launched, perform a manual rescan for updates by selecting in the menu bar Apps > Check for Updates (⌘⇧U). This will regenerate MacUpdate Desktop's scan data and those apps should show up again.
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