Welcome to the forum.
Lightroom 4 only works on the operating systems OSX and Windows Vista 64 and Win7-64. It does not work on iOS, Android or Linux. iOS and Android so not have enough hardware horsepower to run Lightroom. While Linux could run Lightroom, Adobe has not compiled a version for this niche OS platform.
In January, I upgraded my iPhone to the 4s. I walked out of the Apple store with an iPad too. Two montha later, I was back to pick up an iMac. This is my first OSX product ever. I've always been a Windows person, primarily because I required Windows applications in my work. I'm retired now and that is no longer a requirement.
If you are looking to move to a Mac, the iMac with a 27" screen is very appealing. I think most people opt for the MacBook Pro - portable but a smaller screen. While you could run LR4 on a MacBook Air, you may be disappointed with the performance.
I use iCloud to integrate my iPad and iPhone photos into LR. I replaced a Windows Laptop with the iPad. I had LR running on the aging Laptop, but it was not essential. I now use the iPad in the field to preview my work and for Quick and dirty edits (using iPhoto or PS Express. Both read my RAW image files imported from the camera)
