Well, usually the controls are a pretty big distinction. As you've noticed, keyboard and mouse is generally a lot more precise and has a lot more buttons than a controller, which means games invariably end up 'streamlined' (euphemism for 'stuff taken out', it's not always bad, but the term has been coloured by it being used to describe the exorcism of generally a lot of good features.)
This means what you get on a PC game is usually a port of the more profitable console version, this often means a: the graphics are worse and b: the controls are WAY worse, because they're optimised for an analogue stick and other controller features which can take an unnecessarily long time to navigate with a mouse.
See, another reason for this is that the rise of consoles has kinda directly correlated with the fall of really hardcore PC titles. For example, take the RPG. The main example - the 'bioware RPG' as a kind of subgenre.
The bioware RPG used to be praised for its attention to detail, long and engaging stories, and complex gameplay - epitomised by the game 'Baldur's Gate' When consoles became more prominent, Bioware moved to a more KOTOR style - a lot of graphical flourish and voice acting, but still pretty solid gameplay mechanics, a complex plot, etc. Everyone (obv not EVERYONE but still) regarded this as a great step forward. Then along comes Mass Effect. Mass Effect is the dividing line. Obviously designed for both consoles and PC, Mass Effect rips out the complex combat mechanics of preceding bioware games and replaces them with point and click shooter mechanics and a very very simple conversation wheel with obvious, literally highlighted 'best options' in the form of renegade and paragon options.
The sound of a thousand hardcore RPG fans screaming out and being suddenly silenced can be heard about this point.
Before the persuade mechanic was a matter of luck and skill - a gamble that could pay off, or backfire, and this made it interesting. Paragon and Renegade are however 'win conversation free' buttons. It's a great game, but it's also a watermark title. EVERYONE (and again, not really everyone obv) jumps on the 'simplification' train to Mass Effectsville, and why? Because it worked for the console gamers. They lapped it up. Whereas the dry style of a Baldur's Gate or a Planescape torment is not something you'd ever see on a console, Mass Effect manifestly is. This means anybody who wants to make money had better cut out the idea of an old school RPG or be prepared to fling Bioware levels of money at it to 'triple A' it in other areas. See Dragon Age - Whilst a very engaging RPG with a huge plot, solid dialogue and expansive conversation arcs, interesting characters (matter of taste I guess, but this is personal opinion) and all sorts of other tropes the hardcore RPG fans identify as their own, one of the biggest problems people had with dragon age is that it takes a 'consoleish' approach to spells. A fireball is a fireball is a fireball. How much damage does it do? Not telling. This hex, what does it do? Well it decreases resistance. By how much? Not telling. Well that's gone down like a lead Hindenburg with the hardcore RPG crowd who once more see a truly promising RPG watered down to the simple standards the console crowd demand. Whether or not that's anything to do with the game being out on console has become irrelevant - the very act of 'not telling' is seen to be associated with the 'streamlined' nature of consoles, and so the blame lies at their feet.
Anyway, this rage reached apoplectic levels when DA2 was announced with the following news: More streamlining. Instead of those brilliant origins, they're gone, leaving you with Boring Mchuman-Chinpants III (or his invariably better voice-acted female counterpart who bioware won't acknowledge) So features = removed. What of the combat? Ah, well they seen how well ME2 done, and so now they'll be changing the combat to be more 'action oriented'. Features = removed. Instead of a branching, complex conversation tree, we're being given the fully misleading and voice acted wheel, where you have to hope for the best that what you click is actually what you end up saying. Feaures = removed. By this point, 'dumbed down for the consoles' has become the scapegoat of choice. every time a developer has noticed console games seem quite profitable, a complex game vanishes to be replaced with a point and click blast/gorefest.
And there you have it. A short story, incoherently told, through the medium of a single developers game creation process, of why we call console games dumbed down.
