I also think it depends on where in the spectrum of retirement you are. I think if you're a couple of years away, focusing on paying down the mortgage is helpful because the time for compounding is much less, but the effect on reducing your expenses (the other half of the equation we at ER.org get, but many others miss) is huge.
For someone like me, still 5+ (and probably more) away from retirement, living in a home that is probably not our "forever" residence, with a 5/5 ARM that's only one year in, paying it down quickly doesn't make much sense. First, the tax deduction helps keep us in the 25% bracket. Second, the 2.875% interest rate vs. "expected historical return" on our portfolio (around 8% incl dividends) with - as mentioned - at least five more years until retirement mandates (to me) that we stay our present course.
While enticing to potentially pay off the mortgage in four or so years (fund tax-advantaged accounts, then apply all else to principal), it doesn't make sense to me to lose those years of additional accumulation and especially compounding while we have stable income in order to possibly lower expenses in the future. Maybe we'll be in the same house... but I doubt it.
Of course, when the market returns -10% over the next five years, I'll regret this decision.
And if we're still in the same house in six years, we'll re-evaluate based on the interest rate change.