You have several reasons. First, DSL is definitely not a symmetric
allocation of bandwidth (the most deployed version is ADSL which is by
definition assymetric) which means that upload and download speeds are
definitely not the same. If an ISP does have the abiltiy to allocate
bandwidth symmetrically they typically don't simply because far more people
download content then upload it. Throttling the upload speed enables the ISP
to offer better download speeds for everyone. Another reason is simply just
because you have a pipe a certain size doesn't mean you can utilize it. The
server you may be posting files to is, itself, busy doing lots of things so
your publish may not be that high of a priority, or it may be processing the
information as fast as it can and doesn't want to go faster. Because you are
communicating to another device that may be busy doing it's own thing or
could have it's own limitations on connection speeds you will rarely, if
ever, receive anything close to the maximum upload speed for a site.
Also, the connection speed can be misleading. A very good ISP will have
about 6 mbits/second bandwidth available to you. Your Ethernet connection
however won't show that amount since it knows nothing about it. It only
knows the speed it negotiated with the device it's plugged into. If you're
plugged directly into a cable modem or a router, your connection speed on
the computer will show exactly how fast you can be connected to that
particular device. 100 mbits/second is the typical connection speed for a
modern ethernet device (unless of course it's a Gigabit Ethernet device but
there is no need for a cable/dsl modem to have this connectoin speed simply
because you won't be getting that much bandwidth). So, your Ethernet icon
will show 100 mbits/second but in actuality you may only get 6 mbits/second
or lower. Lots of DSL plans are really only 1.4 mbits/second or even lower
at about 700 kbits/second.
Hope this helps,
Mark Fitzpatrick
Microsoft MVP - FrontPage