There are two reasons why this may be the case. Firstly, the programmes available to install differ on each Office 365 package.
Secondly, it depends whether you are installing on a PC or a Mac.
Office installation on a PC includes: Access, Excel, Lync, OneNote, PowerPoint, Publisher, Word
Office installation on a Mac includes: Excel, PowerPoint, Word
Also for a Mac, you can download OneNote from the Mac App Store for free, and you can use Lync 2011 alongside your Office 365 package if your company is already using this.