They were banned because too many people were using 'lag machines', there only enabled for VIPs and mods, you can see how to become a VIP here. http://www.sandlotminecraft.com/index.php?pages/vip/
You must have donator rank to use redstone. Creates income, ya know? Without some restricted things, we couldn't keep the server up.
Actually, cheracc stated that this is because VIPs have an incentive to keep the server running, so would not make lag machines. It is in no way P2W.
An unseen, unlocated lag machine once led to an entire Creative map eventually being wiped. Everyone's work, gone. The lag was so bad it was even affecting other worlds. Limiting redstone to VIP's was an attempt to not remove it altogether.