Google indexing less sites then submitted in sitemap

I built a simple clean website which has only 7 pages. I have a siteamp.xml and have submitted it to Google Webmaster tools. It shows 7 pages submitted, but only 3 of the 7 pages are indexed which helps to explain why the ranking is poor. It is not like I have 500 pages and only 470 are showing up. The site is three month old now, so although it is newer, it is not all that new.
I have built a number of websites, but this is the first time I am seeing this. Any thoughts?

See original post by Packerland