I think Tetris is an ideal candidate for web delivery anyway. Then you get a nice and small download - mainly just the images and sound - offline support, mobile support, much easier accessibility (just a URL away), and greater chance of viral marketing/sharing. Why would you want to weigh that down with a desktop app? Modern versions of Windows even stop you running a downloaded EXE if it's not run often, for security reasons.
You cannot rely on WebGL being present in node-webkit either. Node-webkit basically is Chrome, and just like Chrome, WebGL support is subject to driver and hardware blacklists.