Chris here…
Here’s a thread from WordPress’ own forums which seems to be a similar problem to ours: http://wordpress.org/support/topic/wordpress-site-loading-extremely-slowly .
To give you a bit of insight into why it may happen…
On a “static” website like ThunderCats Lair is now, the site is basically a collection of actual HTML pages that are created on one of our computers, saved and then uploaded in the same way that someone would create, save and upload a picture, a video, or whatever. The pages that we upload sit on our web server and when someone clicks on a link, that web server presents that web page to the person who has requested it… 
WordPress sites work differently in that whenever we create a new page, what we are effectively doing is uploading content to a database. Each page is treated as an entry into the database. When somebody clicks on a link to one of our pages, they send a message to the web server, which instructs the database to retrieve the information for that entry (i.e. the HTML code, text, pictures, etc.) - so, all web pages are actually being generated “on the fly” as someone attempts to access them… 
This very message board actually works in exactly the same way, and is powered by PHP / MySQL - the same programming language / database combo that WordPress is powered by! 
In theory, with a powerful web server, there shouldn’t be any significant latency issues when it comes to the server generating and presenting web pages. However, ThunderCats Lair is a MASSIVE website - so, if the server that this site is sitting on is suddenly getting a lot of traffic for some of the other websites that occupy the same server space (remembering that this site is not sitting on its own unique server - if we were we’d be paying a hell of a lot more for our web hosting), I can see how that would slow down a site like ours that is extremely large and (in the case of the WordPress version) makes a lot of calls to the server… 
A site that’s powered by WordPress that is much, much bigger than ThunderCats Lair is eBay - however, eBay is almost certain to be sitting on its own dedicated web server (God knows they can afford it) and so there are no other websites competing for the resources of that web server. 
So, to summarise - I actually think the problem of the slow-loading site lies not with WordPress (even though database-driven sites will be a half-step slower than old-fashioned websites) but rather with our webhost (Hostmonster)? It wouldn’t surprise me to discover that the slow loading times we’re encountering are to do with another active database-driven site (or two, or three) being assigned to the same server that we’re on - to me it’s the answer that makes the most logical sense! 
…All of which is probably a far more technical answer than you really wanted, LOL!! 
Take care… 