After all, they're both online text editors. They're also both document publishers, though by default Docs doesn't display your document to the world. They both have general document management, including tagging, though Docs also has version control. They both allow collaboration, though Blogger does it through comments and Docs through 'sharing'. They both allow insertion of images and hyperlinks, though in addition Blogger allows videos and Docs allows tables.
None of these differences are major - in fact, I can see most of them being eliminated at some point through general upgrades.
So why do Google have two different applications?
Different uses, same appThey're different because of their history - they're from different cultures. Word processing comes from years of office work, with deeply embedded notions like folders, separate files, and the A4/letter paper size. Blogging comes from an online free-flowing diary format, technically minimalist, constantly added to, and aligned to the computer screen.
That doesn't excuse the basic user interface confusion between the two systems, for example the different ways to edit the underlying HTML. At some point, surely, the solutions must converge.
I can't see that the functionality requirements are different - it's just there are two different uses. Perhaps it's fine they're branded differently, like Proctor & Gamble owning several major washing powder lines to segregate the market.
While blogging tools start to take on advanced word processing features, document tools like Google Docs will improve in "content management" - versioning, publishing, collaboration, tagging, etc.
Surely one tool that can handle both blogging and word processing will emerge soon.