I don't think it would be all that shocking if they remained 13th in the league in defense.  After all, that's not even in the top 3rd.

The Giants have a number of pitchers who might not fit the DIPS model.  Zito definitely has shown the ability to keep it substantially lower than .300 and Cain has been south of .300, and greatly so, while in the pros except for his first season, which was cut short.  Ortiz was also south of .300 much of his career, though it is too soon to tell if he's actually able to still do that.  And Lincecum certainly looks like a sub .300 BABIP pitcher as well, based on his minors stats, though obviously not by today's game line.

Less hits means you can have a higher BB/9 (and thus K/BB) and still do well as a pitcher, particularly since BIP accounts for something like 60-70% of all plays and hits do more damage than BB.  I forgot where I posted stats but I took each pitcher's reduced

Morris doesn't strike out a lot anymore but he has demonstrated over this career that he can keep his BB/9 down low and, once he lost his velocity, got his BB/9 down even lower.  This season has been an aberration in that he's walking a lot more than usual, but has been extremely lucky in keeping HR/9 and HR/FB way down low.  Each should approach his career means and counteract each other as the season progresses.  In addition, since he's become a low velocity starter (2003 on), his BABIP has been on the lower side, though not dramatically so, but that's not necessary if you walk at a very low rate, like he does (mid to low 2's when 3 is good).  The thing is, he's capable of a high 3 ERA, low 4 ERA, based on his peripherals, and he was there last season until the very end when at some point he got injured (and should have DLed but kept silent).

Lowry I've been worried about because he hasn't had a high K game since his strained oblique last season, but this last game with 8 K's and 1 BB tells me that he's got his changeup working again and he'll be like he was in 2005 and not like how he was in 2006.  Last season and this season, until his last game, highest he could strike out was 6.  In 2005, 12 starts out of 33 that he had 7 or more strikeouts.  In fact, he was slow starting that season too, he didn't hit 7+ strikeouts until May 6th, so he's right on target if 2005 is what he's capable of.

So I like the Giants rotation a lot, both long term and for playoff success.  Pitchers like Cain and Lincecum can be dominant when they are on, and Zito, Lowry, and Morris have good outings many more times than disastrous ones.  That's why I like the Zito signing, because it made our rotation pretty top notch relative to most teams, he was the tipping point from a good to a great rotation.

If you examine how the rotation compares to the majors, they are basically a rotation of #2 starters (see The Hardball Times articles on starters by slot by Jeff Sackman).  BP noted that Zito, despite his negatives sabermetically, is the top or #2 starter on most rotations (see 2007 comments on Zito).  Cain had a high 3 ERA after his skipped start and clearly has been doing well this season.  Lowry had a high 3 ERA in 2004 and 2005 and, as I noted, he seems to be rounding into 2005 form.  Morris, was a low to mid 4 ERA last season until the very end when he was pitching injured.  Ortiz, who knows now, but he was a #2 type previously but even if he isn't, Lincecum gives us hope that he can be something like a #2 if Ortiz isn't.

That's a rotation full of #2 starters (or possibly better) that will be hard for any team to get through, during the season or in the playoffs, leaving it up to our offense to just be average and that will win us a lot of games if they can.  After their slow start, they have been average and we have won a lot.