Arjonius
Legend
Silver Level
It's not hard to build a BR at the lowest levels, just slow when measured in $ or $/hour. Yes, you pay a higher % in rake, but you also have more fish handing you money.So that advice isn't so much that new players should always play $100NL or above, but that playing lower makes it very difficult to build a bankroll. There are other benefits to playing lower stakes, like cutting your teeth in the games or having slightly profitable fun if you have a massive edge on the competition; but, for building a bankroll, players are generally better off starting with a large enough amount to risk to avoid the rake totally eating their winnings.
Assuming a person has the ability to win at NL100 or above, his roll will almost certainly grow faster than at NL2, 5 or 10. But that's quite an assumption for most players, never mind relatively new ones.