You shouldn't see "Full length" PCI-cards in desktops - I haven't so far. It's really just something for servers - and then it's usually something like a solid quad-channel RAID-controller or something like that.
It's just marketing BS for desktops - I've not seen anyone need or use a full-length PCI card in a desktop yet.
Marketing - they'd even sell cars with "features" such as:
* Steering wheel
* Wheels
* Gears
and so on ... (detected the cynicism, did you)

. Either way - it is not something you need to worry about unless you're playing with servers

.