I'll point to 10 important distinguishing features:
1. You can see exactly where your files are in LR (even with "referenced" files in Aperture, that's impossible/impractical)
Agreed, that's a primary philosophical difference between the way the two programs are organised. Lightroom's internal organisation mirrors the organisation on your disk. Aperture's internal organisation is completely independent of your disk. It can be set up to mirror it if that's your preferred way of working, but that's never as transparent as it is with Lightroom. On the other hand, Aperture's independence of the organisation of files on disk permits organisations based on logical structures rather than physical ones, and so is more flexible.
2. LR works on PC or Mac, so you're not forced to buy one brand of computer, can easily change, and have access to a far bigger pool of knowledge and support
3. You can process large numbers of images much more quickly using LR's Auto Sync mode to adjust multiple images with a single mouse stroke (much more efficient than copy and paste or lift and stamp)
Lift and stamp is slower, but not as much slower as you might suggest: select all images, one mouse click to bring up the lift-stamp box, one more to apply it to all selected images. I've just moved from LR3b2 to Ap3 and I find the two operations basically the same. So I wouldn't agree that it is MUCH quicker. Marginally quicker, perhaps.
4. The Before / After view splits the screen and is excellent for fine tuning your adjustments.
Yes, this is certainly easier in Lightroom. Aperture can quickly swap between the master image without adjustments and the version with adjustments (just hit M) but it is not as nice as split screen for detailed comparisons.
5. The "targeted adjustment tool" allows you to make adjustments by dragging over the image, so you keep your eye on its appearance as you're working
6. Even months later, you can use History steps to restore images' previous appearance
7. You can apply split tones to black and white pictures
8. Camera profiles enable you to mimic cameras' built-in picture styles and apply alternative rendition of the raw data, as well as creating your own
These are nice features of Lightroom which are better implemented there than Aperture.
9. Moving work between computers is simple
My experience is that Aperture 3's new library handling actually puts it ahead of Lightroom here.
10. In LR3, the noise reduction is astonishing
Yup, so if you shoot lots of high ISO noise-ridden images, that may well be the killer feature to decide in favour of LR regardless of other shortcomings.
I do mostly base ISO work lit with studio flash so Aperture's much better retouch, skin smoothing and other local adjustment tools plus the generally greater coherence of its user interface for my way of working, swung it the other way for me.