To understand why the system works like it does, you need to first understand that Slashdot is about to start accepting new ad formats. The large ads that you see on many other sites are coming here. We really don't have an option: these are what advertisers want, and if we don't provide them, we won't be around much longer. But we want to give you an option to see Slashdot without these ads. Second, you need to understand that Slashdot readers fall into a variety of types, and charging the same flat fee just isn't possible.
Slashdot subscriptions will essentially let you buy a thousand pages to be viewed without banner ads. And you will have some flexibility to decide what types of pages (Comments, Articles, The Homepage) you want ads removed from, and what types of pages you just want to see the ads.
The rates are currently set at $5 per 1000 pages. To put this into perspective, $20 (typical magazine subscription) will be enough pages for 82% of our readers to view Slashdot without ads for a year. Another 15% will need to spend $5 a month to accomplish the same thing. 3% of our readers would need to spend more than $5 a month- but they could choose to see ads on comments and in almost every case, still pay around $5 a month. (As an aside, it's also worth noting that more than half of all comment posters fall into this 3%)
We realize that this system is more complex, but Slashdot has a third of a million readers per day with different reading habits, and this is the best way to accomodate everyone fairly.
Currently we only accept payment via paypal. It was simply easy and fast. We intend to offer other options as time permits and readers request.
Eventually we intend to offer additional features to subscribers. Exactly what those plums are remains to be decided: Access to the rejected submissions bin? A 'Gold Star' in your comments header? Karma? (I think that would be hilarious) We really don't know. We'll decide and implement what makes sense as we have time to do it.
We are doing our best to learn from the mistakes made by other sites that have started charging for subscriptions. We won't create subscriber only features that cost more to maintain than they generate. But we do need support from you if we are to continue. So anyway, here's that link again if you forgot it ;)