I don't think they can by writing hubs alone, but Hubpages is an awesome place to start building a following while polishing your skills. Think of content like any other product -- you can't make a household name by only putting products in consignment shops, or by producing items that are then branded by another company. You can get really good at what you make, and you can get a lot of feedback about the product, but few will actually know it's you. Using the knowledge gained from operating within someone else's domain, however, it is possible to then go on and write books, develop your own website, write some killer marketing copy, or whatever other part of the writing world you may want to tackle. I do think that sites like this can be an extremely valuable part of the journey toward becoming a renowned writer, it just can't end here.