Blame it on the Au-Au-Au-Au-Au-Autotune.

Ok..so these two performances were done within MONTHS of each other (the one at the bottom being the most recent one). Now, a lot of people are saying that Rihanna ISN'T using auto-tune in the second one but if you listen CLOSELY (especially at 2:17 and 3:00-3:01), and then compare it to the first video performance which took place in November I believe(?), then you'll notice a HUGE difference in Rihanna's voice that sounds almost, AUTOTUNED. Now, before you guys jump down my throat let me say that Rihanna has grown TREMENDOUSLY in the last couple years as far as live performances, but there's no ignoring the use of auto-tune here.