television ratios joke. 4:3 became 16:9 for widescreen. Further from square and closer to the "golden ratio", so make something closer with different prime squares.
In reality I was joking about fashion. The new trend in monoliths is a metallic finish and slender proportions, skipping one prime square - The original is 1²:2²:3² and the new one is 1²:3²:7² (skips primes 2 and 5). The dimensions continue, of course. In Clarke's 2010 it's kind of assumed it'd mean it'd be integers, but the new one fits better with primes.
The monolith in 2001 had dimensions in ratios of 1:4:9 [and continuing into other dimensions...].
Why the heck would you go to all the work of putting a monolith of the wrong shape out there?