Adblock Plus is indeed effective for 90% of the adverts/banners, but only if it is installed. That raises a few issues.
The first is if you are using a machine where you don't have administrative rights to install extensions (eg. work, public terminal, someone else's machine), or a device for which it is not or only partially effective (some phones, tablets), then the ads are a nightmare.
Most regular users tend to have installed an adblocker as they know how crap the site is without one. The second problem is not the regulars though, its the first time visitors or occasional browsers who are put off from joining, you can't assume they have all got ABP and so the site gains a poor reputation and atrophies as a result.
Thirdly, the basic principle of covering a community fan site in adverts to line one person's pockets is fairly dubious in itself. I doubt anyone would object to sponsorship or donation-based funding to cover a site's costs, but AbMad is clearly out to make money for one individual. Even then that would be fine (in a free market kind of way) if it provided a service above and beyond the "free" options, but it doesn't.