Reply #99: they explain that on the website since you are buying a pixel

[NMDemDist2]

Everyone is welcome to buy our pixels, which are available in 100-pixel 'blocks' (each measuring 10x10 pixels). You will see the homepage is divided into 10,000 of these 100-pixel blocks (hence there are 1,000,000 pixels in total). The reason for selling them in 100-pixel blocks is because anything smaller would be too small to display anything meaningful.

You can buy as many pixels as you like, as long as there are some available (see the live stats in the top right corner of the page). When you buy some pixels, you can then display an image/ad/logo of your choice in the space you have purchased. You can also have the image click through to your own website. However, no obscene or offensive images are allowed.

The pixels you buy will be displayed on the homepage permanently. The homepage will not change and will be tied to the station we secure as our home, and will remain forever linked as the founding sponsors. In the long run, the pixels will offer good value and you will be part of internet history in the making! ......

Why can't I buy one single pixel?
You can't display anything meaningful in one pixel - nor click it easily - so visually, it would be pointless. With thousands of random tiny colored dots all over the place, the site would look horrible.