From Soh (Linode) in the comments [0]: "We’ve deliberated and brought the floor for all plans to have 1000Mbps. Thanks for your feedback!"

So it appears that 75Mbps was the initial speed but after some internal deliberation (possibly influenced by feedback), they raised it to 1000Mbps.

[0] https://blog.linode.com/2017/02/14/high-memory-instances-and...