Yes, 4.5 turnovers is a lot, but is it that far ahead of Deron Williams' 4.0, or John Wall's 3.9, or Kevin Durant's 3.8? And it's a lot less than the "10" you quoted (hence the exaggeration).
Lin has played a mere 64 games in his NBA career. He's a newborn baby by NBA standards (covered in gross after-birth with the umbilical cord still attached). The assumption is that he'll cut down his turnovers in due time.
If Bayless is retained, it'll be because Barbosa was unavailable (as a scoring option off the bench). After all, Colangelo wouldn't go on the air saying that he needs a PG if he honestly thought Bayless was the guy.