WhatsApp is now available only for iPhone.
The messaging app "Whatsapp", is no more available for the iPod and iPad because of a decision taken by Apple, and it has now removed from the App Store for those devices. Now the WhatsApp App is only available for iPhone.
While WhatsApp for Android is free, WhatsApp has a price in the App Store, and Apple is not refunding the amount of any previous purchase.
WhatsApp keeps working on those iPad and iPod devices in which it is still installed. But you won't be able to update or purchase WhatsApp for iPad or iPod anymore.
Those iPod and iPad users who had already purchased it and who want to keep using it in the near future will be able to do so as long as they don't erase the installed app, and as long as the installed version remains compatible enough, because there's no (legal) way to get a WhatsApp app for your iPad or iPod.
You can create a backup of the app syncing the device with iTunes in your own computer, and then copying the file "WhatsApp.ipa" located inside the folder: "C:\Documents and Settings\Windows username\My documents\My music\iTunes\iTunes Media\Mobile Applications" (in Windows XP; other newer Windows operating systems store the app data in a similar route).
Note: that files has a unique ID, and works only in the device in which the original purchase of the app took place, as it is synchronized with the user's iTunes account. Copying and pasting that WhatsApp data file in a different iPad or iPod will make the app to stop working.