I do not have an Xbox How do I stop W8 asking me to log in for every simple game I want to play - e.g. solitaire

Why can't people just answer the question asked!  You didn't ask for an alternative, to avoid your problem, you asked how to fix it!  And then offering suggestions that MIGHT help, but don't, instead of ones that actually do help, are simply misleading.

You CAN get this problem to go away, but you have to jump through a stupid Microsoft hoop to get it to go away.  This problem was plaguing me as well.  I just wanted to SIMPLY PLAY MY GOOD OLD WINDOWS 7 Solitaire, and it lead me through all of this heartache and I ended up here, with this problem too. 

(Microsoft needs to do a lot more research on their "Intuitive Interface" for Windows 8 and learn how to lead people to change properly, without irritating them and taking things away.)

To get rid of this irritating plague, you need to sign-in with your Microsoft Account (a.k.a. (also known as) Windows Live ID, and many other names), creating your XBox games account, using the XBOX games app.

1. Start the green "Games" app, which should be on your default Metro start screen, if you haven't removed it.  It has a white XBox controller on the green square.
2. Once that app is running, at the top right, just as in the Microsoft Solitaire Collections app, there should be a sign-in link that you can click on to sign in.  Use your Windows Account to sign-in. 

Once you have your Xbox games account signed-in, it will assign you a generic user name for your Xbox account.  You don't actually have to have an XBox gaming system to have an XBox game account for Windows 8.  (You can create an avatar for your XBox game account while you're signed-in, but don't get tripped up by Microsoft again like I did when you click on your avatar and wonder what to do next.  Once you choose your avatar, you have to (unintuitively) click the check box below the avatar to actually select it.)

3. From the Metro start screen, click on Microsoft Solitaire Collection app (assuming you added it there.)
4. Notice that the Microsoft Solitaire Collection has always attempted to automatically sign-in to the XBox games account when started.  Since we didn't have the XBox games account setup, it irritated us with that annoying authentication window every time we simply wanted to play.  Now it should automatically connect and no longer irritate you with that authentication window.

Here is another obscured tip, to "sign-out" of the XBox games account, in case you too were wondering how, but couldn't intuitively determine how from the intuitive interface:

To "sign-out" of Xbox games do this:

a.      Open the Xbox games from start screen.

b.      Press Windows key+C and select Settings.

c.       Select accounts and You will get an option to sign out.

d.      Click on sign out.

I believe that Microsoft is now requiring  an Xbox live account to play games within the Xbox Games app in Windows 8. I'm almost certain that an Xbox device isn't needed in order to use the Xbox live services.

As you play games in the Windows 8 Xbox app, statistics and achievements are recoded to your Xbox live profile. These can be games on a phone, PC, tablet or the Xbox console itself.

If you download and install traditional games via the desktop or install games with a service like Steam, then you would be bypassing the Xbox app altogether and would not need to sign in with an Xbox account.