Dave,
to be frank, you're missing nothing.
Like countless millions of other people who are still buying brand new PCs with Windows 7 installed.
The difference between 8 and 8.1? Well, the difference is purely down to cost. If you are offered two completely identical computers, but one has 8 and the other has 8.1, then if the one with 8 is cheaper, that's the one to buy. ALL computers with 8 installed are fully eligible to a completely free of charge upgrade to 8.1, via the internet.
The choice between 8 and 8.1 is soooooo simple.
However, the choice between 7 and 8 is more difficult.
If you want a steep learning curve, have little experience of computers, love your mobile phone, learn how to cope when things happen / pop up / open / close, which you don't understand or didn't want to happen / pop up / open / close, and like to be at the cutting edge, then Windows 8.1 all the way.
If you grew up with computers, Windows 95, XP, 3.1 even, perhaps zx81, then you have two options.
Firstly, if you "just want it to work" in a way in which you are familiar, then forget Windows 8 or 8.1 and go for 7.
Secondly, if you are happy to "tinker", then get Windows 8 / 8.1. If 8, then immediately upgrade it to 8.1 before doing ANYTHHING else. Set 8.1 so that it "boots to desktop". Then, I strongly recommend installing some freeware called "Classic Shell" which will give you a very familiar Start button, complete with access to programs, control panel, My Documents, My Pictures, etc. etc. even a shut down option! When installing any other software, it is helpful if you always allow the installer to "create a desktop shortcut". (Without a desktop shortcut and without Classic Shell, then starting your new software in Windows 8 / 8.1 is a blooming nightmare of searching for a needle in a haystack).
If buying a laptop with 8 / 8.1 ALWAYS buy a mouse. The touchpad becomes possessed by the devil with 8 / 8.1. The touchpads now respond to two finger actions. Such as touching the pad with two fingers, then moving those fingers apart or moving those fingers together. It also opens hidden menus on all four edges and all four corners of the screen if your finger either "swipes" the touchpad from a corner, or an edge. Touchpads are sensitive, so even if you only touch the pad with one finger, but the second finger hovers really close to the pad, or accidentally brushes the pad, then all sorts of silly things happen on screen. The view zooms for no reason, or menus suddenly appear for no reason, or the damn Metro thing appears for no reason. Using a separate mouse DOES avoid all this.
I started with an Atari 520STFM, progressed to Windows 3.1, missed 95 to go straight to 98SE, was appalled by ME, loved XP, didn't see the fuss and was happy with Vista, then bought a laptop with 8. After 2 days of frustration with 8, I ripped 8 off the hard drive and installed Vista with NO regrets at all!! When 8.1 was launched, I decided to give it a spin. Found it was little different to 8, but then decided to install Classic Shell, then connected a mouse and I've been a happy chappy ever since!
Hope that helps