I wish they'd sort that out (WhatsApp not this apps dev). It's kind of ridiculous there web app only works on one platform.
They blame Apple for that. Limitations.
Only because their web client works via the phone, and their whole service is based on having a phone number; they should do a more commonplace username/password based logins (with maybe two-factor authentication on a phone) and have a regular, proper client. It's probably the biggest chat tool out there; surely they can afford to build a native client or two?
As Cthulhu_ says it's more to do with the design of their app than iOS. Now that they have the clout of Facebook behind them they should be able to come up with a solution.
Why would you not just run WhatsApp if you have an iOS device? You want to run it as a secondary client?
Actually, it would be possible IF you device is jailbroken, but I rather not.
I'm wondering until when we'll have to wait. That shit man.