Re: 2013 MBA vs. 2013 MBP as secondary web development computer
If portability is your primary interest, the Air will very much be of interest to you. What it lacks in power, it makes up for in weight and battery life. If you already have a primary computer at home to do your heavy lifting, you won't miss the extra performance the MBP provides.
The Pro is very much a stand alone system, it is powerful enough that you really don't need a desktop computer. It has worse battery life and weighs a lot more but has excellent performance.
The 2013 Macbook Air has an Intel HD 5000 integrated graphics chip which can reserve up to 1 GB of system RAM for video. While the performance won't be as good as a specced out MBP, this should be more than enough to run Photoshop with 3D effects and such. You might want to consider investing in extra RAM over the 4GB though, depending on what kind of web development work you do.