I had the same question, so I went to the website and then to the customer support "live chat". The person from the manufacturer said the only difference was the attachments. In fact, it has the same manual for both models.
I own two different models of the Shark vacuums - Navigator Pro - purchased in Feb 2013 and Navigator Lift-Away - purchased a week or so ago. The cleaning path, amps and attachments are the same.
The differences between the Pro and the Lift-Away:
The Lift-Away has a suction control dial, which is nice depending on what you are vacuuming. Area rugs get sucked up often with these vacuums because of their amazing power. the Lift-Away allows you to easily adjust that, so it doesn't happen.
The Lift-Away has a swivel head which makes it easier to vacuum around furniture, corners, etc. The attachments are the same on both vacuums.
I am completely sold on ANY of their vacuums and would choose them over any Dyson out there (for instance). My only problem with the two I've purchased is that the third attachment - the rotary brush for cleaning pet hair from furniture - does not have a place to store it on the machine. That just seems silly to me. With my first purchase, I tried sticking it to the machine with velcro, but that didn't work so well because of all the movement you are putting the machine through when vacuuming. But it's definitely not a deal breaker for me!! I hope this helps! :)