I assure you its very different from the vast majority of business plans out there. Here is Dropbox's YC app:
I do think the plan you linked to is more thorough than what the majority of SMBs will be writing. YC is another league of finance. Most SMBs I know are not very sophisticated
It also included a background check on the management IIRC
Can you link to an example SMB business plan? I once tried to help a neighborhood grocer with financing and I can assure you they weren't writing a sophisticated business plan.