Earlier quoted context omitted.
I wouldn't necessarily frame that as an inevitability of Dropbox as a product, as much as an inevitability of the traditional VC funding model. It's likely you could build a very healthy business selling people file syncing — I personally use a tiny minimalist Dropbox competitor that seems to be doing just fine. The hypergrowth demanded by investors when you take on $1.7B in funding is what's the challenge.
This was one of the biggest takeaways from the "Startup podcast". If you haven't heard it, it details Alex Blumberg (of this American Life fame) attempts to create a company producing high quality long form podcasts. At one point he and his partner are getting excited that they are on the road to profitability in 6 months. One of their VCs gets upset by this saying that targeting profitability is a sure way to end up…
If you're not aiming for this kind of territory, you're not really compatible with the VC financial model, which is designed around high risk and high reward. 30–40% of startups end up in liquidation, and 95% never meet their projections. Unless some your successful companies have fantastic returns, your fund will fail.
This is something you should understand before you take VC money.