Of course, the Rowand deal was on the table at the beginning of the season, before we knew exactly how good the rest of the bullpen would be.
Perhaps Kevin Towers wasn't quite as sure whether or not the pen could withstand the loss of Linebrink yet.
Going into the season Heath Bell was a guy who posted a 5.59 ERA and a 5.11 ERA in the two previous seasons, for example.
By the time it became certain that we could do without Linebrink I'm sure the Rowand deal was off the table.
In short, it's easy to use hindsight (something you claim to not use...) and say he should have traded for Rowand when he had the chance, but I can certainly understand the hesitance to do so at the time the deal was proposed.