Some of this is because many PC gamers think of the PC in a traditional sense: Desk/monitor/keyboard/mouse.
With the way that modern technology has become so heavily streamlined for home use there is little reason why people can't go through the extra steps for more elaborate setups, like having their computer hooked up to their TV/projector and using wireless input device hubs.
The one thing holding that back are the controllers. A console has a very simple, very compact controller, whereas computers have more complex controllers with more comfort issues. (lying back with a keyboard mouse vs lying back with an xbox controller. ) Its a double edged sword though, because one of the major complaints many PC gamers have against consoles are the limitations of the controllers themselves.
However, you're starting to see a shift in this over time. Originally there was just the plain old keyboard/mouse. Then people started making more advanced mice for gamers. Then you've started to see more advanced keyboards. Now, finally, you are starting to see purpose built peripherals for PC gamers, like the G13 game pad (which is amazing by the way.)
Joysticks are a real history lesson in the history of peripheral advances, as they were the first (thank god for those flight sim nuts.) You started with relatively basic stuff, but very quickly you started to see *very* advanced peripheral hardware coming out. Force feedback joysticks started showing up in what, the mid 90s? I bought my dad one right around then I think..... And when you think about the tech in those they were *very* advanced for their time.
It very well could be the case that, as time goes on, more streamlined peripherals come out that are more suited towards the "laying back" gaming attitude
And the only reason this is true, which is also the prime difference between consoles and PCs, is the freedom of the development market. Understanding it as a darwinian system consoles are somewhat inbred. They innovate in a vaccuum without much, if any, competition (when it comes to peripherals). PCs are like the pile of muck behind my fridge though, its a breeding ground for innovation due to the freedoms they have, and for that reason are quite likely to move farther, faster than the console peripherals (which really they have done 2o times over.)
Long story short, PCs have the oppurtunity to do exactly what consoles do, while the reverse isn't true.
btw check this out for "laying back" gaming:
http://theairmouse.com/