I too like to hear why people voted the way they did, I mean all three are solid systems that gen so any vote is down to almost petty reasoning. (Although I could understand a person voting for the 360 if they where on the 5th system and just had a horrible time with the machine.)
Petty reasoning or not, the whole point of this poll is to choose the system that was least satisfying within the last generation. That doesn't mean the system was bad, not by any means, they're all pretty solid in their own ways and they all have their flaws.
The Wii was underwhelming from a technological stand-point and aside from Nintendo exclusives and a couple notable games it severely lacked in the triple-A department and the multiplats were obviously the worst on it since it was the weakest out of the three.
The PS3 had the most juice but it was so complex that you needed a degree in rocket science to program for the thing, hence the library is relatively small, but nevertheless filled with good content that's worth picking up, that, and it offered great multimedia capabilities and had the latest optical drive - shame that the controller was very meh and their implementation of motion controls never really kicked off like the Wii's did.
The Xbox 360 was like the middle ground between the two - the CPU was based on CELL technology in the sense that the cores were modified PPE's, but the whole architecture was steamlined and memory was unified which lead to more releases, especially early on in the life cycle. Xbox Live was also the best implementation of online, however on the flip side it is a paid service to this day which can be a turn-off... and then there's the Kinect - a futuristic dream that sounds fantastic in theory... but doesn't exactly deliver in practice.
All three consoles had hiccups in terms of reliability - the Wii had the blue slot of death, the PS3 had the yellow light of death, the 360 had the red ring of death, so in that department they all initially had issues, especially the 360 and the PS3, but in the end they were resolved with subsequent revisions.
All in all, it comes down to everyone's personal experience with the systems, which is a good thing - it means the generation was fruitful and every manufacturer offered something interesting to their customers.