It wouldn't. But such islands are typically not very interesting either. The context of who links to a domain is very important for a search engine for many tasks, not just discovery.
Internet arguably doesn't even have a size. You can construct a website that's like n.example.com/m which links to '(n+1).example.com/m' and 'n.example.com/(m+1)', for each m and n between 0 and 1e308.
Dunno about the others, but my crawler has a set depth it will crawl. It'll BFS for like 1000-10000 documents depending on some factors.