Financial planning: What year is it, anyway?

I like to think I'm not a complete idiot at simple financial planning, but some of the stuff out there seems to be just confusing. 

 

This is from the T Rowe Price site, which is generally pretty clear.  I'm 60, so I move the slider so I'm 5 years before retirement (I don't know when I will actually retire, but that's a different story).

 

The site recommends the Retirement 2020 fund. Since it's 2010, shouldn't it recommend the Retirement 2015 fund?

 

But wait. If I move the slider so I'm 10 years before retirement, it recommends the Retirement 2015 fund. But If I'm 10 years before retirement, why wouldn't it recommend Retirement 2020?