The WWW's fundamental job is not to establish consensus. It is to communicate information. Incompatible changes to the web and incompatible changes to the bitcoin protocol have very different significance.
> Its not as if somebodies coins will suddenly become worthless.
I think this is in fact the nightmare scenario that some folks are worried about.
I agree with you it's unlikely to happen, because it's in very few people's interests, but I think that the degree of danger is exactly what's causing people to try so vigorously to find ways to co-operate on this matter.
And it's true that browsers also have incentive toward compatibility. But the fact is, despite this incentive, browsers remain in many ways incompatible. And for the most part, nobody notices, because minor incompatibilities in browsers do not "fork" the web the same way an incompatibility in bitcoin protocol forks the blockchain.
Its not as if somebodies coins will suddenly become worthless.
Bitcoin has a lot of actors. Users, investors, miners, exchanges, shops... And everybody will have some hassle with a fork.
Just like on the WWW where there are webmasters, webdesigners, users, browser vendors, shops... And every has some hassle with browser compatibility.