The difference, of course, is all in the bass. If you are able to integrate a sub to the bookshelf speakers smoothly, the result can be identical to the sound of speakers with larger woofers. I think the subwoofer - introduced only about 15 years ago - has changed everything about the way we think of speakers. The "rules" we had 15 years ago are all out the window because of the sub.
For home theater use, I think the sub is the next most important speaker to the center channel. Once you have one, the size of the woofers in the other speakers becomes relatively unimportant.
My own main speakers, made by Epos, have tiny 6 inch woofers and, by themselves, are very lean in the bass. They are like bookshelf speakers with a longer enclosure. When supported by my sub, however, the sound is exciting and fulfilling. In other words, you can get the job done either way.