It is possible that a HD iPad 3 release will take place in March. Apart from that, it is also possible that the iPad 4 will be released later this year in October 2012. This isn't the first time that we've heard rumours of two iPad being released in one calendar year.
Last year when rumours about the iPad 2 were coming out each day, even back then it was said that Apple will release two iPads in 2011. Given the fact that it was confirmed early on that the iPad 2 will not feature a Retina Display, the premise of this rumour was based solely upon the fact that the second iPad which was supposedly going to release in fall 2011, will come with Retina Display. Since 2011 has passed, we know that none of those rumours turned out to be true.
The rumour comes from a publication called DigiTimes, which has a hit or miss record when it comes to rumours. Citing Taiwanese component makers as sources, this report claims that the HD iPad 3 release will take place in March 2012. iPad 3 will sport a full HD 1,536x2,048 pixels QXGA display, double battery life and a quad-core A6 processor. This very source also claims that there won't be any other significant hardware change. Following the HD iPad 3 release, the iPad 2 price will be slashed down to $399 for the entry level 16GB model.
One might believe what is being said about HD iPad 3 release in March, because like it or not, Apple will release a new iPad possibly by March keeping up with its release cycle. What's hard to believe is the rumour about iPad 4 release in October 2012. The iPad 4 will retain the 9.7-inch iconic form factor and to quote this report. "will have much upgraded hardware specifications and integrated applications". That's all this report knows about the iPad 4 at this point in time.
Though it can't be ruled out that Apple won't release another iPad after the HD iPad 3 release in March. Releasing iPad 3 in March will help Apple keep itself ahead in the already burgeoning tablet market, and by releasing another one in October, it will certainly maintain its lead against all competitors in the market.