I think SEGA is uncertain as to how these IPs will do, Sonic will obviously sell but I assume they are gauging the interest of the 3D games to see which games they should attempt to be more like. However, Sonic Team will probably just do their own weird stupid shit again with evil aliens or something.
Space Channel 5 is not that great IMO, but the sequel is just fantastic. If that does poorly then the series is all but dead.
As Chizzles pointed out, SEGA has been known for not doing arcade-perfect releases, but are usually good at making them work correctly. SEGA Rally Championship, Virtua Fighter 2, 3, 4 and tons of other releases could really stand to have arcade-perfect ports, but SEGA is all but uncertain on how they could sell, if at all. I can understand in cases like this why they would be worried to put so much money into releasing them.