College admissions' focus on social justice has only increased over the past few decades (% of low-income students at the very top universities has only gone up). The proliferation of angel money means that it is actually easier for you to get the connections necessary for VC. In the past, VC was an even tighter and more exclusive circle than it is today.
This does not mean that it is easy, nor common. The measurement is against a low base.
The fact of the matter is that being born lower-class means that it is very likely that you will not move out of that class during your lifetime.
Lots of interesting data here: http://www.pewstates.org/projects/economic-mobility-project-...
WRT the ease of breaking into Silicon Valley, I don't have any basis for comparison. As you may have inferred, I'm a person from a lower class background who broke in during the early-mid-90s and had my life forever changed as a result. Including class mobility.
My anecdotal point above was just that, an anecdotal point.
I only commented on relative difficulty.