This is a phenomenon that I don't understand. An article by Jacob Luft on si.com suggests that the Pirates are shopping Kris Benson because he's in his walk year, and since the Pirates wouldn't be able to afford him on the free agent market, they will probably try to get something in return while they can. He draws an analogy to Jason Schmidt, whom the Giants picked up in 2001 from the Pirates, and the rest is history...
From the Pirates perspective, they should certainly be trying to deal Benson for prospects. Decent starting pitching is always in high demand at the trading deadline, so there should be several teams lining up to overpay for his services, assuming that he isn't injured or doesn't go in the tank at some point during the season. Benson offers the tantalizing possibility that the light may come on and he will dazzle from August to eternity. The Pirates won't sign Benson after the season, and assuming they aren't contending this year, they'd be crazy not to try to get a good deal for him. Of course, they could keep him and get draft pick compensation, but I'm sure as a winning organization they'll weigh that decision appropriately...
I digress. Luft suggests that the Pirates are planning to deal Benson because of their inability to offer him a "big money, multiyear contract". But why, exactly, should Pittsburgh or any other major league team do such a thing? Benson epitomizes the Baseball Prospectus adage "there is no such thing as a pitching prospect". His major league resume crystallizes the difference between potential and performance. He has never come close to the potential he allegedly had, and he has been injured-prone, to put it mildly He's been in the major leagues for 5+ seasons, and his record is, well, ordinary:
-- He's won a grand total of 37 games - slightly more than 7 wins per season. (I know, I know, wins aren't the best indicator of how good a pitcher is, but only 7 wins per season has to mean something, even on a bad team)
-- His career WHIP is a mediocre 1.42
-- His control has been average at best, walking an average of 3.6 per 9 innings in his career
-- He's strikeout rate has declined since 2000, down to 5.5 per 9 innings so far this year (and he's never been a top strikeout pitcher)
Pittsburgh, or any other team for that matter, would be out of their minds to offer Benson a big-money, multiyear deal. Of course, some high-revenue team will probably give him a 4-year, $35 million contract based on his "potential".
Jason Schmidt is a fun comparison because the situation is so similar -- he was a mediocre pitcher with the Pirates too. In his three full seasons with the Pirates (1997-1999), Schmidt had a strikeout ratio of 6.5K/9 inn, which was respectable but not stellar. He was injured for much of 2000 and 2001, so it would have been hard to accurately forecast his future prospects. In his two full seasons with the Giants, he's had 9.3K/9 inn, a dramatic improvement. I'd love to give Brian Sabean all of the credit for spotting this diamond in the rough, but generally speaking I don't think anyone could have expected this much improvement from Schmidt (and it may not last...we'll see).
But its always tough to make comparisons like this, because we're talking about ONE player -- Schmidt dramatically improved, but how many other pitchers with similar potential and history went on to continue with their perfectly ordinary careers? There really wasn't much in Schmidt's history to suggest that he was going to become so much better with the Giants after his stint with the Pirates, and the same goes for Benson -- except that Benson is a highly-touted, overall #1 draft pick.
Benson, of course, could transform himself into a great pitcher. Overall #1 draft picks will get the benefit of the doubt many times over, and he may not yet be fully recovered from Tommy John surgery. He'd be a great pickup for the Royals with an incentive-laden contract, but I would recommend that he stay away for his safety. Given the Royals track record of recent years with pitchers, he'd be injured as soon as he put on the uniform.
Anyway, in more than five years in the Bigs, Kris Benson has demonstrated that he is certainly a major league quality pitcher, but he's not a star, and he's hasn't touched "dominant". At some point, a guy is what he is, and it would be a surprise to see Benson go on to anything besides continuing to be a journeyman major league starter for the rest of his career.