Accessories manufacturers don't have a clue about Apple marketing plans until the very last minute. They usually get the physical specifications for new product versions in advance, so they can have products ready for launch. They also may get information about naming for product packaging, close to the release.
Since the new iPad is being announced next week, it seems that it may be the right time for big manufacturers like Griffin and Belkin to get this kind of info. However, until Tim Cook and his mariachis are on stage next week, we will not know for sure. [Thanks Michael Fonfara!]
Update: A reader reports that a device called iPad HD has been appearing occasionally in Google Analytics since April 2011. However, device names can be easily simulated using Chrome or Firefox browsers. His data also list a 2048 x 1536 device accessing the site during the same period, which coincides with the rumoured resolution for the new iPad. However, this resolution could be a desktop monitor too. In fact, our own analytics show devices with this resolution accessing Gizmodo since 2009, but no iPad HD is to be found in our listings. Just iPad (no iPad 2 either).
Update 2: Scratch that. The reader says the device information is not from Google Analytics, but usage data from an application called Tapatalk, which runs on iOS, Android and Blackberry. This data can't be spoofed (although the data can be doctored in any case). Here's the graphic he forwarded to us:
Here is access data from the month of February.