When to Replace Timing Belt?

[dylar]

I have a 99 S70 and while it is overdue for a timing belt change in terms of years, in terms of miles we are still only at 77,000. The belt looks fine--no cracks or other signs of wear, which was confirmed by the mechanic. The mechanic suggested we replace it based on manufacturer recommendation (you're supposed to replace it after ten years). Is this really necessary?