As fairviewroad said, points are based on ticket cost, not distance.
For most trains, cost is usually based on distance, so you *could* say that points are based on distance, but it's mostly coincidental, and not a tight correlation.
For example, I priced the most expensive accomodation (family bedroom), on the longest single-train journey (Empire Builder, CHI-PDX, 2257 miles), and it was $900, or 1800 points, or .79 points per mile.
My own 6-mile commute home gets 100 (base) points, or 16.7 points per mile.

That said, it is absolutely possible to have either 100,000 or (though less easily) 1,000,000 points, even with modest travel. In about 16 months of Amtrak travel, never even outside of CA, I've earned a little under 75,000 points from travel alone (including elite and promo bonuses), transferred in 40,000 from Continental, and 'earned' a little under 7,000 in other bonuses (Select and Select Plus magazine 'redemption opportunity', a single Choice stay, etc). Had I never redeemed, I'd now have a little over 120,000. Until earlier this month, I'd only redeemed a total of 17,000 (various little 'Special Route' trips), and I'd still have over 100,000, but that I redeemed 30,500 over the past couple weeks (and 30,000 more soon) for tickets for a grand trip in the fall.

In Another Place, a member describes a trip all over the country, and mentions in Yet Another Place that it was mostly redemptions, suggesting he must have simply *redeemed* around 100,000.

Imagine some businessperson (or Senator ) on an expense account, who does an Acela FC 'city-pair' commute to and from work each of the approximately 250 weekdays in a year (500 trips). Counting elite bonuses ([s]he'd be Select after just 7 segments, and Select Plus after 14), but not even any promotion bonuses, and assuming no redemptions, [s]he'd have approximately 560,000 points at the end of that year (but would have spent some $100,000 for them. )
Even if the same person just commuted to and from work on less expensive corridor services like the Keystone or Hiawatha, [s]he'd have around 70,000 points at the end of the year.
And of course, there's the pudding.

But yes, it is not *that* hard, especially for 100,000 points.