Hi Rob,
Can't say for sure about that difference in Office, but I know in the past some of admins have mentioned things that only came with Office in E Plans.
But as I mentioned some of the services which come with the E-Plan make it worth the extra cost, using them allows you to have stunning pages showing live real-time data to employees, even if you have only yourself, they add a lot of value.
And then the number of sites and subs you can create, make for some neat ways to break-up the data in your company and organize it for easy use.
And of course, as I said now with the freedom to mix and match, you do not need to get across the board, many employees can use plans that are less costly.