There were some fairly large gaps, the most notable being the two years or so between WC 2 and WC 3. Mind you, during that break, we also got Academy and Armada.
At any rate, it should be pointed out that you don't make a persistent, online world for thousands of players overnight. And don't bother comparing this to UO, because UO was a totally different system. In fact, Ultima lent itself very well to the concept, because it was already a complete world, and it had a good system for player development.
WC, on the other hand, does not lend itself very well at all.
At this stage, you will all yell "Come on, WC could be a great multiplayer game!". Don't worry. I agree. It could be great. But think of all the issues that have to be resolved first.
Take distance, for example. The vast distances were solved in WC with the autopilot function. Well, guess what? You can't do that here. Autopilot skips time, and that would totally mess up a multiplayer game. Hyperspeed? Great, but it's not WC-esque. Have players fly the huge distances manually? What and make them pay for the connection times when all they do is sit there for half an hour watching space dust fly by? Reduce distances? You want several thousand users. If you reduce distances, they just won't fit. Not to mention that that would also not be WC-esque
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And distance is probably one of the simpler problems faced by the POL design team. Have patience. One day, we will see POL, but that's a long way off.