My #1 core directory site has so far remained untouched however I have seen a lot of movement below it including my core site #2 which has bounced about considerably in the top 20 for several keywords.
I suspect the real answer to your question is that they are blissfully unaware or, if they do know they have reached the top of the SERPs, have no idea how they did it and won't be particularly concerned when they drop again...they'll have had their 15 minutes of fame:-)
Certainly, I have a .mobi site firmly in the top 11~15 for several weeks now. It's a good site and it's applicable however in the regular SERPs?
I just do not expect to see a .mobi site there. Is this wrong of me?