quite common for a "two tier" style membership, forums cost a significant amount of money to run.
The BMW GS Forum I am on has a paid level, access to things like For Sale Forums are restricted to those who cough up £15 a year.
OOF has avoided this, as it creates a "I've paid my money, therefore I'm a better member than you" effect. OOF Shop profits are used to help fund some of the running costs.
In all honesty I never realised there were costs involved to run it. but then again I am a luddite! 
What do you think this software runs on?
We used to use Yabb forum now migrated to this, TheBoy has spent 100's hours working on getting the forum running right, migrating and testing replacements to Yabb. Indexing the site so when you search in Google is bloody hard work, its not very easy to become number 1 in search results. You need a dedicated internet line for the server, you average broadband hookup aint going to cut the mustard.
Time, Money, resources spent on making a server, making sure it has enough power/capacity's to run the 1,000's requests per minute it does.
Then it needs electricity, that costs money. It needs UPS battery backup supplies for spikes/dropouts in electric dropout.
omegaowners.com name need to be paid for, configured, updated when ISP's change their DNS
Does not happen by magic you know
