There's no rule against multiple winnings. In fact, it looks like once you join the winner's pool you're more likely to win again
This is a tech website essentially, so i think there should be a rule like that BUT it should apply from when the tablet was released to the public, the device I won was released in 2011 and has only a 160k screen, that's ancient in terms of tech.Would be kind of nice, in a sense, for people who have won similar prizes to what's on offer to not be eligible for a year's period - in this example, if you won a tablet in Jan 2013, you don't get to win any other tablets till Jan 2014, but are still eligible for anything else (such as a laptop, desktop or even a Lamborgini if it comes to it - just not another tablet)
Otherwise, what would happen in the event that someone wins, as an example, an i7-3770 in January 2013 (released Q2'12), and then a few months later in current time, such as in April (then Q2'13) its successor has come out? It's still an expensive prize, it's still a well-performing prize and you only just won the one you got, which you wouldn't necessarily have had otherwise. Just because it's newer and better doesn't mean people should automatically be entitled to winning 'again' just because what they have is older. Not in my opinion, anyway.
Hell, for a more direct comparison, let's talk iPhone 4 vs iPhone 4S as prizes for two different competitions run in a relatively short span of time. "I should be allowed to take part because my iPhone 4 is old!"? Nein danke.