The Facebook owned WhatsApp recently turned seven. At the time the app started, 70% of the smartphones purchased were powered by BlackBerry or Symbian. Android, iOS and Windows Phone, now installed in 99.5% of mobile devices, was in use on only 25% of such products at the time. WhatsApp says that for the next seven years, it wants to concentrate on the platforms that the "the vast majority of people use."
If you employ a handset that runs on one of the affected operating systems and want to remain a WhatsApp user, the messaging app has a one word recommendation for you, "Upgrade!"
This is an interesting move by WhatsApp, especially the decision to stop supporting the earlier Android builds. We wouldn't be surprised to see other apps follow WhatsApp and start weeding out older Android platforms.
source: WhatsApp via Crackberry