Dropbox was a YC company, which meant they had quite a bit of free press and access to a lot of valley connections. I would imagine that had a lot to do with their success.
Notice this too, on the marketing front: we had issues getting the press excited at launch. We built a fantastic Windows client. 3 years ago, everyone was running Windows . We were so excited to show the press, yet they all had Macs. Walt Mossberg wouldn't write about our product because it was PC only. Months after we hired our PR agency, we found out that they had never even used our product... because they too onl…
B2B needs lots of features, a great sales team, and can be Windows only.
B2C needs a great simple UI (which may one day have lots of power features tucked away, hopefullly after A/B testing), lots of press, and multi-platform is a big plus.