There's nothing complicated about how internet works.
Simple truth: direct streaming from NetFlix of a sample movie (http://movies.netflix.com/WiMovie/Example_Short_23.976/70136810), while also streaming another movie from NetFlix on my Apple TV - 560 kbit/sec maximum. Here's the traceroute to the server from which it's being streamed:
dniq-mba:~ root# traceroute 108.175.42.142
traceroute to 108.175.42.142 (108.175.42.142), 64 hops max, 52 byte packets
1 192.168.1.1 (192.168.1.1) 2.695 ms 1.551 ms 0.965 ms
2 l100.nwrknj-vfttp-96.verizon-gni.net (98.109.218.1) 7.524 ms 6.214 ms 6.285 ms
3 g0-13-2-0.nwrknj-lcr-21.verizon-gni.net (130.81.109.116) 10.986 ms 7.362 ms 8.094 ms
4 ae0-0.nwrk-bb-rtr1.verizon-gni.net (130.81.209.154) 7.664 ms
ae1-0.nwrk-bb-rtr1.verizon-gni.net (130.81.209.146) 6.032 ms 4.657 ms
5 0.xe-10-1-0.br1.nyc1.alter.net (152.63.18.225) 10.493 ms
0.xe-5-0-0.br1.nyc1.alter.net (152.63.16.61) 7.052 ms
0.xe-10-1-0.br1.nyc1.alter.net (152.63.18.225) 39.672 ms
6 * * ae11.edge2.newyork.level3.net (4.68.62.41) 42.052 ms
7 4.34.146.66 (4.34.146.66) 52.443 ms 49.003 ms 47.555 ms
8 ipv4_1.lagg0.c033.nyc001.ix.nflxvideo.net (108.175.42.142) 49.647 ms 49.635 ms 47.286 ms
And then I connect to my work VPN (all traffic now goes via the VPN) - suddenly the speed becomes 3000 kbit/sec. And here's the traceroute again:
dniq-mba:~ root# traceroute 108.175.43.165
traceroute to 108.175.43.165 (108.175.43.165), 64 hops max, 52 byte packets
1 10.11.0.36 (10.11.0.36) 11.397 ms 12.910 ms 10.537 ms
2 10.11.0.1 (10.11.0.1) 9.074 ms 12.515 ms 11.629 ms
3 12.130.81.133 (12.130.81.133) 9.830 ms 12.855 ms 13.381 ms
4 mdf016c7613r0001-tge-10-4.nyc2.attens.net (63.240.24.105) 15.201 ms 12.380 ms 14.328 ms
5 12.122.251.41 (12.122.251.41) 9.978 ms 11.212 ms 12.649 ms
6 cr2.n54ny.ip.att.net (12.122.130.94) 15.857 ms 16.380 ms 14.606 ms
7 igs3.n54ny.ip.att.net (12.122.115.89) 14.208 ms 14.022 ms 14.550 ms
8 ae-15.r05.nycmny01.us.bb.gin.ntt.net (129.250.9.205) 13.816 ms 18.349 ms 13.998 ms
9 ae-3.r06.nycmny01.us.bb.gin.ntt.net (129.250.4.205) 13.600 ms 14.362 ms 13.881 ms
10 ae-1.netflix.nycmny01.us.bb.gin.ntt.net (129.250.198.114) 54.818 ms 56.614 ms 54.739 ms
11 ipv4_1.lagg0.c075.nyc001.ix.nflxvideo.net (108.175.43.165) 48.449 ms 44.598 ms 47.986 ms
And then I disconnect from the VPN again, and stop streaming the movie on Apple TV - suddenly the speed in my web browser improves to 3000 kbit/sec!
So two devices streaming video from NetFlix over the same connection are limited to around 3500 kbit/sec. When I connect to my VPN - Apple TV streams directly from NetFlix, while web browser streams via the VPN. Verizon can no longer see that I have the second stream from NetFlix, therefore not limiting the bandwidth for the VPN one.
If this is not the evidence of Verizon throttling the speed - I don't know what is.