McLane is very loyal to Biggio - some would argue to a fault. Biggio also has more influence on the Astros than any other player in their history. I would argue it's not a PR move (not that it's bad PR - Biggio is loved in Huston), but rather ownership unwilling to consider any other option.
Biggio was just fine in the first half of the last couple of years - it's the wear of the season that gets to him. I think that, as much as anything, was way Loretta was brought in - they're not counting on Biggio for the whole year.