What per cent of companies pay all of annual 401 contibution at year end?
One consequence of one payment in mid-December each year is that if an employee quits before then he loses the matching for that year. Another change will be a savings to IBM from the use of cash during the year until 12/15 -- that's a step back for employees as the yield to them will go down.
It doesn't look dumb to me. If I were an IBM'er I would not like it. You have to assume that the IBM BOD would not have approved it unless the supporting research made sense to them.
I'm sure if I were an IBM'er that the change per se would not be enough to make me jump ship.