It still begs the question, what advantage would there be for a twice yearly iPad release?
It's not a twice yearly rumor, it's a twice
this year rumor.
The advantage could be that Apple simply has something nice ready to go early in the year and something nicer ready to go later in the year (just like laptops, iMacs, etc). Maybe some killer technology advance is not quite ready for Spring but will be ready for Fall and Apple would still like to upgrade a nearly 1-year old device sooner than Fall.
Maybe there was always a plan for iPad1 & 2 to be spread out for a year but 3 & 4 to come in the same year?
If we see iPad as still ahead of all competition, we can imagine 3 as maintaining that lead. A 4 arriving only 6+ months later could be imagined as another big leap out ahead. If we see iPad as being competitive or slightly behind some other hardware, maybe 3 brings parity or jumps back ahead and 4 leaps far ahead.
Maybe iOS6 brings some innovative new feature that requires a hardware change that can't yet go into iPad3. For example, maybe iPad3 with 3G hardware because Apple doesn't yet like the LTE options, and iPad 4 with iOS6 brings LTE? LTE is already increasingly available in competitor devices. Would Apple really want iPad 3 (with perhaps "old" 3G-only) to still be THE iPad until Mar 2013?
Maybe Apple has got a thorough whiff of some innovations coming out at CES or before Mar, 2013 and has accelerated their cycle in response.
There's a few for you. I'm sure there are many more.
In a nutshell, 2 versions this year only "doesn't make sense", "is stupid", etc only until Apple rolls out 2 versions this year. Then, we see iPad4 in late 2012 as "genius", "best iPad ever", "my credit card is ready", etc.
Personally, I very much like that other Apple tech is updated more than just once each year (I don't like potentially paying full price for 365+-day old Apple tech up to the day before it is updated with brand new Apple tech). For example, if Apple upgrades laptops, iMacs, iPads or iPhones THREE times in 2012, it would be fine by me. I can appreciate the desire that what someone buys is the latest for a year, but I personally don't buy so I can brag about having the latest- I buy for utility, what Apple tech can do for me, etc. If a 3 is desirable I'll buy it. If a 4 is desirable, I'll sell the 3 and buy it. However, I can enjoy the 3 until there is a 4 and not feel bad that I didn't wait another 6+ months for a 4 that may or may not show.