Yeah, I found it odd that the iPad left out some native apps that the iPhone came with. Off the top off my head:
Calculator
Weather
Stocks
Voice memo
Alarm clock/timer
I have no idea why, and it was pretty annoying at first. Sure, there are free apps that could take their place, but you'd more than likely have to put up with annoying ads unless you purchase the premium version.
There are a bunch of simple free calculator apps on the app store. You might have to deal with pop up ads though.