The choices I see are:

     (1) Do not correct the 5 and cause people to misidentify the logo at small sizes since it looks like a 6 then

     (2) Correct the 5 at the cost of an almost imperceptible change in small instantiations of the logo

     (3) Redesign the whole thing to use a font that is distinctive at all sizes

Between (1) and (2), I feel that (2) is always the winner. (3) appears to beat them both, but it means prioritizing distinction at small sizes at the same level as style, text color, weight, and any number of higher level and arguably more important factors. I feel like this exact tradeoff was done by the designer and their choice of (2) very well founded.

Wolf Olins is a particularly good example of the fact that brand is far larger than logo. I'm not even a particular fan of this new HTML5 brand, I feel like it overemphasizes and romanticizes a tool, but I won't get caught arguing that it's not comprehensive, or strongly suggested by all of the proposed instantiations on the website, or to weak to survive the likely numerous changes it'll suffer should it be widely adopted.