In the <b:includable id='post' var='post'> that is a child element of <b:widget id='Blog1' .. it simply says:
<div class='post-body'> <p> <data:post.body /> </p> <div style='clear: both;' /><!-- clear for photos floats --> </div>
Uhmm, that's real easy to change and I can't understand why the template is like that. This leads to another question that I've been thinking about
Are all the template markup the same?, which can be rephrased as are all the customization done with CSS and the related variables?
This template is Minima Blue and changing template to Minima Stretch didn't change this but that's not a real good testcase since part of the template magic is that the widget's and their configuration stays eventhough the template is changed. I had to try another blog so i picked the next one which turned out to be Eric Hill's who's using Rounders 3 and it's just the same, so I'll conclude that it's a general configuration and a general bad idea :-).
I'll try changing it another day, but not right now when I've rewritte the post markup of several of my postings. I will then change permanently to Minima Stretc because it's simpler and easier to read black on white and not the least because it stretches to screenwidth.