The bone spur is the RESULT of the aberrant stresses that are put through whatever is pulling at the bone - the bone spur itself, in the vast majority of cases, does not itself hurt nor is it the CAUSE of any pain. If it's poking something important, like your spinal cord, well, then that's a different story.
If your bone spur is located underneath your heel, pointing towards your toes, it is the reaction of your calcaneus (your heel bone) to lay down more bone along the insertion of the connective tissue (in the case I mentioned, your plantar fascia) in order to try to stop it from pulling away from the bone itself.
The previous poster is correct in that there is no inflammation in plantar fasciitis. Or in any tendon problem, actually. It is a degeneration and disorganization of the tendon or connective tissue, and because of a serious lack of blood supply, it is slow to heal (if it ever does). Injecting these things with a corticosteroid does NOTHING in terms of healing - you may feel great for about 6 months, then you'll either get better because it was going to get better anyway, or (and this is the most common response) you'll actually get much worse than you were before.
And for the love of all things holy, will you people STOP getting things x-rayed and MRI'd???!!!!! You cannot see pain on any image. You can see structural changes, but those IN NO WAY correlate with pain. Unless you just stepped off the curb and broke your ankle, an x-ray will give the MD absolutely NO information whatsoever. Yep - you've got a bone spur. So do about 75% of people who have their feet x-rayed, whether they have pain or not. A bulging disc? Yep - about 60% of people who have never had back pain have bulging discs. Arthritis? Of course. 100% of the population over the age of 50 has it...and the vast majority of them don't even hurt.
Why do doctors tell you these things? Because a) it's all they know how to do, b) there is very little knowledge of pain science outside of certain specialities, and c) they make their money by injecting you with steroids, cutting out bone spurs and sewing up rotator cuff tears and snipping menisci in knees and fusing spines.
Sorry. I've had a really long day, and if one more person comes to me saying they have a "bulging disc" and that's why their back hurts I'm going to strangle someone. Probably Doug, just for fun. I'm sure he deserves it for something anyway.