Dreamcast had a modem that was supported by very few games. There was an optional Ethernet adapter that's very rare and supported by even fewer.
The ethernet on the PS2 was optional until one of the later hardware releases. Very few games were released using it until after the PS3 had already shipped.
The ethernet on the PS2 was optional until one of the later hardware releases. Very few games were released using it until after the PS3 had already shipped.