Those are advertised and theoretical speeds. Just like "100Mbps" ethernet doesn't give you 100MBps actual transfer rates, the telcos and cablecos use weasle words such as "up to" or "as much as". The hardware and line may be capable of sustaining a 2Mbps connection outgoing from your home, but that doesn't factor in things such as TCP overhead, throttling, network congestion, etc...
256 v.s. 2000 is a bit extreme, but I'd suggest checking if your ISP is throttling per-connection speeds - try two uploads at the same time. If the effective speed on both drops to 128, then you've really only got a 256kbit link. If both sustain 256kbit, then you're being throttled on a per-connection basis.
1Unless you're actually getting that kind of throughput, you might want to change the capitalization on the speed measurement (MBps reads as Megabytes, whereas Mbps reads as Megabits). – happy_soil – 2011-03-22T01:41:04.950