As you've probably noticed, the Giants' strength is their pitching staff; yes, their relievers are good, but most especially their starters. When you've got Tim Lincecum and Matt Cain and Madison Bumgarner and then Ryan Vogelsong pulls a Vogelsong ... well, then you've really got something.

But for how long, though? Lincecum's signed through 2013, after which nobody knows. And Matt Cain's eligible for free agency even sooner; eight months from now, he could be gone. Of course the Giants would like to keep him. But according to Ken Rosenthal, the talks about a contract extension aren't going so well ...

Cain’s representatives spoke Wednesday with Giants officials, and the two sides failed to make progress toward a deal, according to major league sources.

No further discussions are planned, sources said, increasing the possibility that Cain could become a free agent at the end of the season.

--snip--

Cain, 27, is seeking a contract that will reflect his position as one of the top pitchers in the game. As a free agent, he might command a deal of at least six years and $20 million per season.

Matt Cain's really, really good. Better than most people understand, I'll wager. You know, because he's never won more than 14 games in a season. Over the last three years, though? Cain's started 33 games in each season, and his 12.3 fWAR ranked seventh in the National League, right between Josh Johnson and Cole Hamels.

Hamels, by the way, is another guy who hasn't won a huge number of games but has a huge payday coming after this season. But we digress ...

It's important to look at more than one season, because what Cain did last season almost certainly is not sustainable. After allowing 22 home runs in both 2009 and '10, he gave up only nine home runs in 2011. Cain did induce more ground balls and fewer fly balls last season, but not nearly enough to account for the dramatically lower home-run rate. I mean, just think about that ... nine home runs all season. Oh, and he never gave up more than one homer in a game; nine games with one home run allowed, and 24 with none at all.

Probably not sustainable.

Matt Cain is an excellent pitcher. But according to FanGraphs, the 2009-2010 Matt Cain was not worth $20 million per season; more like $15 million.

Now, of course that's a baseline figure. He might be worth $10 million to some and $20 million to others ... but to most, somewhere around $15 million. Even if we account for natural salary inflation -- or unnatural salary inflation if future TV deals are as lucrative as advertised -- it's hard to push Cain to $20 million of value per season, especially when we consider the injury risk.

So as good as he is, he does profile as perhaps the Giants' third-best pitcher, if they retain Tim Lincecum beyond 2013 and Madison Bumgarner doesn't get hurt. Can the Giants afford to commit $120 million to their No. 3 starter, with so many projected holes in their lineup?

If Matt Cain's agent really is holding out for that sort of contract, then it's no wonder nothing's happened yet.