In every generation, the console which had the largest pirate game market has won.
In NES vs. SMS, NES had tons of pirate cartridges coming in from China and other Far Eastern countries, so it won.
In Genesis vs. SNES vs. PC Engine, SNES and Genesis pretty much tied for first place, with cartridge readers / dumpers equally available for both systems.
In Saturn vs. PSX vs. N64, PSX won by a mile due to the ease of pirating its games.
Currently, with PS2 vs. Gamecube vs. XBox, PS2 is again winning by a mile due to the ease of pirating its games. Gamecube's proprietary media format and XBox's reverse-burned DVD's are nonstandard, raise costs, make piracy difficult, and therefore make these consoles an unattractive choice for first adopters. This will lead to their failure if history is any indication.