I do try to read the first chapter and then skip to the latest chapter or somewhere in between to check out changes in art (by zooming through the pages without reading so things don't get too spoilerish). If the art stays the same throughout, it doesn't really turn me off personally. But like many others in the webcomic world, I love to see improvement 
Though I only do this when I'm not sure whether to subscribe to a comic or not - not so much for the art but for story. A bit like having a short glance at story progression to see if there's anything eye catching and whether it's worth continuing. Changes in art can be hard to tell, depending on how old the first few pages are compared to the latest.