This is only partly true - there are developers who take "standard" distros such as Ubuntu, PCLOS and probably others, and turn them into much lighter distros. Some Ubuntu-based examples are Crunchbang, which runs fine in just 200 MB RAM so should work better than Xubuntu on an 8 year old laptop, and U-Lite (was Ubuntulite) which is similar but harder to install, and might work in less RAM.
These distros do have full security updates because they are just variants of the main distros. Crunchbang even includes Flash, Java and so on.
The challenge for these older machines is video - many people expect to be able to see Youtube these days. Really the only solution longer-term, as video becomes higher resolution, is to use the older machine as a thin client - LTSP and many other solutions are quite handy here, and the free VMware server makes it quite easy to centrally host Windows images for thin client use within the home through VNC.