If a samsung phone detects that the data pins are shorted (either in the charger or in the cable) it will draw much more power from the charger. If the pins are not shorted, it will only draw 350 or 450 ma. It's their way to get people not to purchase generic chargers

In most instances it's the charger that shorts the pins for some Samsung and Motorola brands, the cable can't be used as a data cable if the cable shorts them.

It's also sort of a safety check so the device doesn't draw too much power from a charging port that can't supply it.

This does not apply to all phones or devices, as many will draw whatever power you give them without having the data pins shorted. Other phones however will only charge at a faster rate if they are shorted.

There are tons of pages online showing how to modify cables or cheap chargers into fooling the phones.

As to the cables, cheaper cables with thinner wires, or longer cables may offer too much resistance to allow a fast charge. Shorter cables, thicker wires, offer less resistance and you are not giving up as much energy to heat up the cable.