You need to ask Adobe. We are a Photoshop user forum.
You can only purchase Photoshop CS6 outright. $700 Standard/$1000 Extended That version is a few years old, will not be upgraded except for Adobe Camera Raw and possible OS fixes. Only one language and one platform (Mac or PC) per license.
The Photography Plan is a $10 per month rental plan. You download CC and CC 2014 as you would CS6, but activation is dependent on the monthly fee. If you stop paying, it stops working. You get upgrades as they are piped through, you can activate on a Mac or PC simply by signing in and the interface can be in almost any language you need.
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Photoshop costs more while the photography plan costs £8:70, does the photography plan have any restrictions or limitations?
I assume you're comparing the Single App Photoshop plan $20/month with the Creative Cloud Photography Plan $10/month?
If that's the case then, no, both versions of Photoshop are identical in those plans.
You obviously get more included with the Photography Plan: Lightroom and Lightroom Mobile making it the obvious plan to get.