Brief history of calibre:
1) Reverse engineer the SONY PRS 500 as it could not then be used on anythong except windows and with anything except the craptacular SONY software
2) release as libprs500, a library to interface with the PRS 500
3) Write html2lrf as a platform independent way to create LRF files. At the time there were probably a total of 100k LRF files in the world.
4) Write a GUI to manage ebook collections and interface with SONY readers.
...
Having support for additional formats doesn't hurt and since I don't maintain them (they're maintained mostly by user_none) I'm happy to leave them in
