Except your math was wrong because you exaggerated the gain for a single damage [W] while not showing the true value of the crit range by ignoring much of what it multiplies. My pali runs around now with 4.5[w] and cleaves for 3 or 5 more and likely has more +[w] bonuses I can't think of right now. Another +1[w] is of a lot less value to me than multiplying all those other +[w]'s as well as my strength bonus and my +11 enhancement bonus and every other base damage bonus and my seeker bonus (that I don't get at all on non crits) by 3 10% more often. Even if they take imp crit away from the bonus I'd rather that 5% more often than an average 5 extra base damage.
Here is a closer approximation of the values. Falchion = 5 average damage, 15-20/x3: 13x5+6x(5x3)=+155 damage over 20 swings. One would need to do a mere 38.75 average damage for the extra 2 crits to simply break even. 77.5 without imp crit.
Basically, you would be right for about the first 4 levels or so and be very wrong as soon as imp crit is had.