Not necessarily. There are still a ton of situations where the iPad is ideal due to its formfactor, but the Air's additional battery is definitely a plus. It really comes down to what you are using the device for.
This was certainly a key factor in me buying one. I have a old 5 year old iMac which has been my main computer and an iPad2 which I originally bought as a portable solution. I love the iPad and it's great for consuming content (i.e.: watching video, surfing, reading emails etc) but it's not great for creating content. Whenever I travel and take it with me I always end up using a friends laptop for writing emails longer than a paragraph or two, sure I could buy a Bluetooth keyboard for it, but that kinda defeats the purpose.
The MBA is going to replace the iMac as my main computer but also be a great solution for travel. I'll still probably use the iPad for watching films on longs flights and for couch surfing (i'd like to even replace it with a iPad Mini for even greater portability) but the MBA will definitely take on more of the tasks I originally bought the iPad for.