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.