In reply to Ryan Hellyer.

You are right but, and it's a huge but, if people are finding w3tc settings confusing they'll get lost with Varnish vcl. Besides, Varnish is only really applicable on VPS or dedicated servers where you have control over what you install. For managed or shared hosting the only real solution is a plugin. If your managed hosting is any good though, they'll do the caching for you.