Query performance

As a test, I ran a query in the pgAdmin query tool, which returns about 15K records from a PostgreSQL v8.01 table on my Win2K server.

I ran the same query from the local server, from another PC on the same 100 mbit local network, and from a PC on a different network, over the internet.

The times for the query to run and the data to return for each of the three
locations are shown here:

• Local Server : 571+521 ms
• Local network: 1187+1266 ms
• Internet:14579+4016 ms

My question is this: Why does the execution time for the query to run increase so much? Since the query should be running on the server, it's time should be somewhat independent of the network transport delay. (unlike the data transport time) However, it appears to actually be hypersensitive to the transport delay. The ratios of time for the data transport (assuming 1 for the local server) are:
1 : 2.43 : 7.71

whereas the query execution time ratios are:
1 : 2.08 : 25.5  (!!!)

Obviously, the transport times will be greater.  But why does the execution time bloat so?