Why would they bother to port/package it?
I've watched the Windows users at work deal with it, and it looks like it's a royal pain, compared to Cygwin+Cygwin-X that I use on the same platforms. It doesn't seem like it's very well integrated into the Windows clipboard, and, at least the version they're using doesn't work with the keyboard shortcuts neatly, either. Maybe they just don't use it well.
For example, with Cygwin, I can highlight and paste with a middle-click, just as on X-Windows, if I'm using an xterm or other X client application; the highlight also populates the Windows clipboard, so I can paste into an Outlook email, for example, using either the Windows application menu edit-paste or the standard keyboard shortcut (CTRL-v).
On a Linux box, I have at least one telnet client, an ssh client (and server, if I want it), various FTP client choices, and xterms, so what would PuTTY bring to the table? 'Bout the only thing missing on most modern distributions is a default xterm readily available in the menu-customization system.
Actually, correct, UNIX-style handling of the clipboard is one of the single best features of PuTTY. Ctrl-V has had a very different meaning in the shell (and vi and ...) much longer than it has had any meaning on a "Pee-Cee". I'd be *very* annoyed if I lost the (in-context) correct meaning of Ctrl-V.
Shift-Insert, copy-on-select. These make sense in a shell-context. I don't have a mouse cursor, and don't want one, within a shell. So, copy-on-select makes sense. I'd never select text and hit paste, like in a windowed environment.