The first reason why this doesn't make any real sense is that it's not easy to write a page about just one keyword phrase with a natural flow
. You are also not using your space efficiently if you only use one keyword per page when you could be using more. Why would you want to optimize for just one keyword when you are able to optimize it for 3 or 4 keyword phrases? The truth is, you are better off using as many keyword phrases as you can on an optimized page. This will bring you more quality traffic. You can find out for yourself by looking at your web analytics that you are getting traffic from several, possibly many different keywords. You will have more success with the search engines if you target a variety of keywords on each page.
It's also a myth that you need to frequently update your site, even though many people believe it greatly impacts your search engine rankings. Spiders will crawl your website more frequently if you are constantly updating it and adding fresh content but it will have little effect on the rank of your site. So, don't make changes that aren't needed simply for the search engines. It will have little effect on them. All you need to do is conduct a search and you will find that a lot of the sites that rank well in niches that are quite popular have not been updated in quite some time.
Generally speaking, the stories we just talked about are quite common but shouldn't make SEO difficult for you. It is vital that you are aware of the facts when you first begin marketing your sites with the search engines so that you don't find yourself wasting time by focusing your efforts in the wrong direction.