I think both are about even is regards to popularity nowadays. It doesn't seem like one has a huge sales advantage over the other. Basically, Tekken was the first game of many to follow Virtua Fighter out of the gate. Soul Blade just didn't light things up the way Tekken did, so they left the series alone for a few years until they could make Soul Calibur on more powerful hardware. Above everything else, it initially got noticed because it was the shining example of 6th generation graphics right at launch. You usually don't get something so damn impressive looking right at the beginning of a generation. It was the equivalent of having Gears of War as a launch title for the 360.
Edit: Correction. I just checked the sales. It seems Tekken is now slightly less popular overall than Soulcalibur.
Tag: Became a freaking mod and a complete douche, coincidentally, at the same time.
