The amount of memory and CPU required for any additional "memory and CPU" requirement for a WP site costs, on a per monthly basis, less than 25% of a single hour for a web developer.
I won't mince words either
Most people who use WP do it for a reason and I think the users who are using WP from the
over 5 million downloads of version 3.2 speak more accurately than the opinion of a user unhappy with his experience on a home server.
Memory is cheap. Very cheap. So is CPU. The CNN web site is run on a Wordpress core...... and I am sure those guys know what they are doing