Cain isn't more consistant than Lincecum.
Lincecum has had a 10.24 K/9 over the last three years. This is phenominal, Randy Johnson 1993-2003 level numbers. Matt Cain has been very good with 7.29 K/9. Cain gives up .86 HR/9 while Lincecum only gave up .53 HR/9. If you move into Fielding Independant Pitching (defense not being a factor like in ERA), Lincecum had a stellar 3.08 FIP while Cain had a 3.26, which is still pretty nifty. However, once you start looking into WAR (Wins of Replacement-level player), Lincecum has been worth a total of 20.8 Wins over the last three seasons while Cain has been worth 11.2 Wins.
Lincecum is without a doubt the better and more consistant pitcher. However, Matt Cain is a severely under-rated pitcher who has brought $80+ million of worth in wins for the low, low price of $1.9 Million per year. Of course, Lincecum has brought in $91.1 Million of worth for the bargain basement price of $400,000 per year (aside from his signing bonus and all).
I know this is beyond what a casual fan cares about, but when looking at roster construction, the yearly budget is the constraint on how much can be spent on the team. The fact that the SF Giants have one of the top 2 pitchers in the NL (Top 5 in MLB) and a pitcher that would be in the top 20 of all of MLB all for $2.3 million..... Its a big reason why they were able to win it all. Now, if only they had brought Buster Posey up earlier in the season, they wouldn't have had such a nail-biter to make the playoffs. Stupid that they ran that sort of a risk just to push back his arbitration eligibility back another year.