And even if they don't do a head-end split, they will usually create a
separate feed to your computer in your home with a filter at that point to
specifically block the (often digital nowadays) TV content bandpass to
prevent interference.
I know of three different cable companies - Comcast here, Cox for my
father, and some company in Illinois (name escapes me) - that don't do
any kind of "splitting" or "filtering."
My coax is split after leaving the wall (regular splitter); one feed
goes to the cable box and the other directly to the cable modem. I
plugged the cable modem line into a TV and got channels, so no
filtering there!
Same for the other two connections for the other two companies.
I realize that this is hardly conclusive evidence, but three different
companie in three widely separated geographic regions does present a
good argument.
Oh, by the way, what does this have to do with the group: WinXP
general advice? Nothing methinks.