Hmm now that's odd. I wonder why that's so fishy for everyone? For me it wouldn't work w/o the www. and for you fancy it just wouldn't go through. Now that beats me. Where's all our tech-heads at? Lord knows I don't speak a lick of technology!
It's, basically, because the internet doesn't have a central server which tells everyone where everything is. Depending on where you connect to the internet (or where you decide to look if you're really advanced), you will go to a certain server to find out where things are. So you enter pleoworld.com into your browser, and it will connect to the given server and ask where pleoworld.com is. Something like a address book or phone directory. These servers send updates to eachother when things change, but it might be a while between a change in one server and that change being sent on to other servers. So, when pleoworld moved from one server to another someone told a few of these servers that pleoworld can now be found at a different point than before. From then on, the new information would start spreading around the globe until all servers are updated. Until they get updated, though, servers will keep sending browsers to pleoworld's old location. So that's why some of us could reach pleoworld sooner and others later, we just happened to ask for its location from a server which had got the new or old information.
Hm, did that make anything clearer?

The servers are called Domain Name Servers (DNS), they're mentioned sometimes here and there so it might be fun to have a grasp of what they are.