Don't know if you've been conned, but I have a 160GB hard drive and I get 149, my brother has a 160GB hard drive and he gets 149, and I think that's about right. You should be getting 93% of what the manufacturer says...
The only thing I'm not sure about is that yours is external. Both listed above are internal. If those work in the exact same way, then you should be getting 149.01, and in that case, you could have been conned.
just for a side note...
1000*1000*1000 = 1000000000
_1KB _1MB__1GB
1024*1024*1024 = 1073741824
1000000000/1073741824 = 0.931322574615478515625 (about 93%)