It's nice to have a long term horizon of a hundred years of mining, and it's true that web-mining can achieve a higher decentralization than any other method. However, at the moment there is still one fundamental element which is totally centralized, and this is your website, where the people can mine. Should your server disappear, so would the network. And obviously your server cannot plan to be online for the next 100 years. How are you planning to solve this critical issue?
Yes, anyone can import our miner&wallet in their website only adding 2 code lines. But the safest place to mine WebDollar will be our website for avoid scam.
That's fine, I guess most of the people will and should mine on your website. However, it's also a matter of scalability. In case of mass adoption, or just only of a few hundreds of thousands of users, sooner or later one single website would start to get some serious problem, unless you'd multiply your servers just like facebook and google do. However, if webdollars will make their whole course and exist for decades then again it will be important that also other sites can mine for the network.
But of course now that you mention it it's clear that other websites can very easily setup scams, and that will happen FOR SURE. So you'd better already think at how to fight that.