Why does something like the Padres turning down closer Huston Street for Tigers' starter Rick Porcello matter to the Red Sox? Well, it might not matter to the actual Red Sox, but there are plenty of armchair GMs who have contemplated moving, say, Andrew Bailey to the Tigers in exchange for the 24-year-old Porcello for months now. It wasn't necessarily a long shot, either, as the Sox are willing to move anyone if they think they will get value back, and a starter with two years of team control left would have more value to them than a reliever with the same.
That being said, if Huston Street is what the Tigers are aiming for, then Bailey surely won't do. Yes, Bailey has two years of control left, but he missed most of 2012 with a thumb injury, and while he only pitched for a short time, he wasn't very good when he did. He's in a situation where, if you already have him, you absolutely hold on to him and hope for a return to form, because said return could be spectacular. If you don't have him, though, it's tougher to negotiate bringing in a potential problem like that, especially in exchange for your most marketable chip.
Street missed some time in 2012 as well, but he still managed to throw 39 innings, make the All-Star team, strike out nearly 11 batters per nine, post a 4.3 strikeout-to-walk ratio, and post an ERA of 1.85. Sure, those numbers would likely go up in Detroit without any Petco assistance, but let's not act like Street isn't awesome at his job. The dude owns a career 3.50 ERA with the Rockies over 167 innings, and his career ERA+ is 145. Health is his most-significant concern, but Bailey isn't going to be the guy you turn to in order to fix that particular issue.
In addition, Street is not only under control for 2013 and 2014, but the extension he signed with the Padres also added a club option for 2015 -- each of those three years costs just $7 million. Bailey is cheaper at just $4.1 million this year, but the presence of the option and the more recent track record of success suggests that there's little chance the Tigers would say yes to Bailey by himself if they're looking more for someone like Street.
It's not a definite -- they shifted sights to Luke Gregerson after Street, and while he's very good, he's no Street. But chances are good that the Tigers are looking for more than the Red Sox might be willing to give up from their bullpen, since they really don't have to trade Porcello for anything, especially not when they could just stick Drew Smyly in the pen to help their bullpen out anyway.