Pellegrini is very low key, even at Málaga where people adored him he didn't like to draw attention to him.
<a class="postlink" href="http://www.youtube.com/watch?v=LwxZ3sG4TZs" onclick="window.open(this.href);return false;">http://www.youtube.com/watch?v=LwxZ3sG4TZs</a> ] This happened the week Málaga was eliminated from the CL and his mom died ( a very emotional game btw)
1:59 You can see that his players had to ask him to come back to the pitch so fans can express him their gratitude.
Maybe another reason because there wasn't an official presentation is that song City fans sang the day of the FA cup final about Pellegrini. That story was reported by many southamerican (especially chilean) and spanish (mostly malaga based) media. I watched it on tv, and of course, the Pellegrini out twitter campaign that the guy from the mancini advert started has also been covered by chilean media(not many tbh), so if you consider that his family lives there it makes sense if he is a little apprehensive .
Probably he is not sure what was the reception he was going to get from city fans after that.