For example, the random series of events that occur while moving through the city early in the adventure provide an interactive (instead of narrative) way to establish the atmosphere of the city under attack. As for the weasel... well, if I used xp, I'd award it for analyzing the situation and deliberately deciding to skip the encounter.
I think the important thing to realise here is that these encounters take up five minutes of your game at most. In my campaign they worked out really well to quickly portray the "city under siege" environment, but if you don't like them - WotBS is a campaign which does not hold you by the hand. A WotC adventure might lead you from room to room or encounter to encounter; we try provide enough information for you to adapt and adopt.
We've never made a secret of the fact that this series is for experienced DMs. Our goal is to create a story, but in a way which a DM can improvise, adapt and explore to his/her desire. Thus that series of encounters is clearly not plot-critical; it's merely a scene-setting series. If it's not to your taste (and there's no way it can be to everyone's taste - as it happens, it was to mine), then it's structured in a way that a DM can do whatever he likes.
There are options to simply narrate the atmosphere if you prefer. But it's structured in a way that you can easily deviate.
You'll find this repeated all the way thorugh the series. We're never going to lead you from room to room and encounter to encounter. We trust you to take your game to the next level and to use the information and ideas to run the game you like, not the game we like.