Here are some examples of startups that did very well focusing on one marketing technique (and some who are still doing it). While I am not privy to why they chose the technique they did, they are all consistently improving over time.
First is Priceonomics. I am a huge fan of any company using their network data to create content that helps their prospects understand the market better. I am personally not sure why more companies dont do it. Priceonomics essentially uses data about prices for used items that it indexes on the web and shares it both on their blog and with key bloggers. The data that capture is turned into both blog posts and informative content. For example how to avoid getting your bike stolen or the Used TV price.
Second is Admob (now acquired by Google). For the longest time the only marketing they would do was research reports on how their ad network was being used. The AdMob mobile metrics report was as highly regarded as the quarterly research report put together by investment banks on specific companies or sectors. These research reports were initially emailed to subscribers quarterly and then they moved to hosting them on Slideshare.
Finally in the initial days of Buzzlogic (now acquired by Twelvefold Media) would put together Vino diaries (video interviews with top influential people in social media). These videos would focus on specific questions and were fairly short.
Bonus tip. How guest blogging propelled one site from 0 to 100,000 users.
Closer to home, I have heard from Krish of Chargbee mentioning that their primary marketing is helping answer questions on key online discussion forums and my own previous company BuzzGain which only focused on guest blogging for large well known marketing influencers as the only technique to gain awareness.