They've produced some really nice visualisations showing international company structures http://opencorporates.com/viz/financial/index.html
Also, it's unlikely that LinkedIn would want to focus solely on early-stage startups since at this point in their trajectory there probably isn't enough money in that category to justify an additional LinkedIn Premium tier.
CrunchBase is immersed in the startup ecosystem and their Business Graph will probably provide and quickly return more relevant information based on their existing dataset.
I think that helping individuals to build their own graphs is really really powerful - and thin that into a "company I am working for now" role relationship / recruitment tool is where the money is
Hmm - I might just have an idea ...
hmmm, that still sounds like LInkedIn but its not what I am after...