I noticed from alexa.com that your site is fairly new - 1 year old. My experience in SEO is that Google likes new sites, but I always thought new meant under 3 months old. Maybe your site has not been indexed until recently. This would explain your good rank. If this is the case, your site should lose its good position at Google, based on experience. Not a big deal, everyone goes through it. This is character building, right?

Another thing that comes to mind with your ranking at the top 4 engines is that Google takes longer to get good rank, in the long run. I do not know, but maybe your site did well once at Yahoo, msn and Ask?

The thing to do now is to keep making your site search engine friendly. Rankings go up and down, unless your site is a Fortune 500 company. In that case, true popularity is king.