GT540 is not getting 2.2 from LG due to the stupidity of the users.
LG seeming lied to users saying that LG Optimus series can't run 2.3 due hardware restrictions. However, Android lead dev brought the lie to light. And, after user uproar, LG has agreed to upgrade Optimus series to 2.3.http://www.engadget....ad-angry-horde/
All the Optimus phones in US ship with 2.2 and are getting a 2.3 upgrade but GT540 is still running 2.1.
Hardware spec wise, all these phones have the same 600MHz processor. Coming to RAM, GT540 has slightly less RAM compared to others in the series. However, Optimus T by T-Mobile still being a T-Mobile version of GT540 ships with 2.2.
If you go through the Google's guidelines, you will notice that there's no such hardware restrictions. Android is open and it has no hard pressed hardware requirements which GT540 cannot meet.
If there are more users willing to take on LG for not supporting GT540, hopefully, they will roll an update.