It looks like Google is willing to experiment even with sacred elements of search, like displaying 10 results per page. The guys from Search Engine Land and SEOMoz started spotting last week some pages with only 7 results.
Here’s a link to the Search Engine Land article talking about it: 7 Is The New 10? Google Showing Fewer Results & More From Same Domain.

Apparently only 20% of search queries are displaying this behavior, though, and the reason might be connected with sitelinks. Those are the extra, smaller links you get when you search for the name of an authority website. It seems that Google wants to clean those pages a bit, as the sitelinks themselves already add a bunch of extra links.
Another theory is that Google wants to give more value and real estate to authority websites, as displaying only 7 links allow them to dominate the first page for some search queries. Here’s a quote from the SEL article:

Indeed, back in the middle of 2010, Google made it official that in some cases, sites might be able to dominate all the results then expanded this later that year.
Now, it feels like another expansion is happening. As said, that’s not directly connected with the shift from 10 to seven results. But it does mean that potentially that brand sites will have an even easier time than ever before to “push down” negative content.
Google recently covered that it’s been working on changes to both sitelinks and site clustering (its term for how it groups pages from the same site). Both shifts covered may be connected to this. But we’re checking with Google to learn more.

The bottom line remains the same: invest your time and effort into creating authoritative and value-packed websites, as those tend to perform much better over the long term.