Well, the results displayed while you are logged in and while you are logged out are different because when you are logged in Google prefers to show you personalized search results. May be the email you are logged with is in someway connected to your domain/ webpage or something that identifies you with your webpage/ domain. If that is the case then Google does not feel it is necessary to show you the results for your page. Also, since you are logged in and since your search becomes personalized, Google will show the results that you've shown interest in...For example, it will show results related to friends or pages (Actors, Music etc.) you have circled on Google Plus etc. (Basically, where Google can identify from the logged in details, who the person is) and so on and so forth...you get the drift.
So, anyway since this could happen to other people who are logged into Google and is searching for your content or keywords, it is necessary to also utilize that area in SEO as well. I mean...if your page or articles (or a link to it) are liked by someone or if Google knows that you are the author of that article and if a friend of yours who has circled you on Google Plus is doing a search while logged in, then Google might show your result first to that person because Google feels that, that person might like to see more articles from you related to that keyword.
Basically, now a days you need to keep an eye on how to optimize the personalized search aspect (along with normal stuff) so that you or your article will appear for a personalized search by someone who is connected to you. So yeah. get your social circles growing especially on Google Plus.
And, the fact that you are still doing all right when you are not logged in, is a good thing to know.