Here is one good reason to keep suburban/urban cats indoors. Mr. Whiskers was hunting Golden-crowned Kinglets along the edge of a ditch.
A variant of another basic reason for keeping cats indoors is provided by Don Gayton in Interwoven Wild, which is an account of the ecology of his suburb and garden not too far from here. Where he lives, crows drop walnuts onto pavement to break them open. Walnuts apparently have a bounce irresistible to prowling house cats, who race onto the road to snatch them, only to be SUVed. The opportunistic, adaptable (vengeful?) crows then augment their nut meal with poor squished kitty.
What a ghastly story. You just made that up, didn't you?
At any rate, I am quite happy to remain inside. Now go away and leave me alone.