I'll get the obvious out of the way first: Brian Sabean has changed. After years of trading prospects to build around Barry Bonds, the Giants have changed up their strategy considerably, but that's not to say that Sabean i totally against trading prospects.
Buster Posey, Madison Bumgarner, Tim Lincecum, Brandon Belt, Jonathan Sanchez, and Matt Cain represent players that have or have not had trade rumors swirl around them in their Giants careers. And at some point in his career, Sabes may very well have pulled the trigger on some of the deals.
Cain for Fielder. Sanchez for Fielder. Lincecum for Rios. Sanchez for (major league shortstop). We've all heard them. Yet I'm pretty sure we're all glad that none of those has happened so far. Anyways, on to the ones that have happened.
So, except in a select few cases, Sabean has done very well in recent years both picking up fringe prospects that have contributed and dumping prospects that may have had value but are on their way out of the good graces of the Giants scouting department. In no particular order:
One of the biggest WTFFFFF moments of my baseball life. I realized this trade was wrong when it happened. I was 14. Pierzynski was a joke, a cancer, and a rental. Nathan emerged as one of the best closers in baseball. Boof Bonser still has as funny name, and is pitching in the Mets minor-league system. Liriano, as stated, just threw a no-hitter and is one of the best "if only he was healthy all the time" pitchers in the American League. Prospects traded, Giants lose.
This was hailed as another Nathan/Liriano trade, except this time the bad guy was an injured but still very friendly Freddy Sanchez, far from being the a-hole that Pierzynski was. Alderson was the number four prospect in the Giants system at the time.
Then Alderson put up this line since joining the Pirates: 14-11, 5.34 ERA, 1.473 WHIP
And Freddy Sanchez did this to Cliff Lee, and all was forgiven.
Prospect traded, Giants win this trade.
Vogelsong was a promising prospect, but the Giants won this trade too, as Vogelsong lost a year to injury, and Schmidt became the ace of the Giants staff. Giants win further by signing Vogelsong to a minor-league deal this year and having him perform well so far.
Yes, part of the Marlins firesales, but Hernandez was the MVP, and the Giants got 746 innings of 4.44 ERA ball, including a few Opening Day starts, for 181 innings of middle relief. Giants win this one for sure.
5. Mike Villano, Joe Fontenot and Mick Pageler to the Marlins for Robb Nen (1997)
Another Marlins firesale pickup, Nen was dominant for the Giants until an arm injury sidelined him for good in 2003. Villano never made it to the majors. Fontenot never made it to the majors. Pageler never made it to the majors. Shades of the Dennis Eckersley trade, in which none of the A's players given to the Cubs made it? I think yes. Giants win.
Giants lose. Nobody knew who Scott Barnes was, but Ryan Garko was terrible.
Torrealba has developed into a starting backstop that has killed the Giants. Foppert was a great story but just never made it out of the injury woods. Randy Winn hit really well for two years and then forgot that he hit really well for two years. I'd say this is a wash.
There are a few more trades that we could look at, but I just don't know where this whole "doesn't like trading prospects" talk comes from. It's right there. He trades prospects more rarely now than before, and when he does, it usually looks pretty smart a little farther on down the road. I would more characterize is it as Sabean only dealing prospects that he knows are going downhill unless their name is Joe Nathan.