"Barcelona losing Messi would be a disaster," he said.
"Real Madrid losing Ronaldo would be a disaster, so this is exactly the same."
He added: "There isn't a release clause in English football, it's very difficult to negotiate with Tottenham and we are not willing to let our best assets go.
Tottenham can finish season well - Bale
"We can't turn this into a debate every time a player does well."
Bale, 23, who also scored for Wales in midweek, gave the home side the lead from a free-kick after five minutes, before grabbing what proved to be the winner with a typical surge down the left followed by a low angled drive.
"It was a great individual performance and it was outstanding to see a player enjoying his football. Gareth is, whatever position he plays," continued Villas-Boas.
"Great teams are made of great individuals too and Gareth is decisive."
Villas-Boas dedicated the win to goalkeeping coach Tony Parks and his son Joe, who was involved in a car crash this week.
Meanwhile, Newcastle manager Alan Pardew said Bale made the difference at White Hart Lane.
"I thought we contained him quite well. We didn't want to open up the goal to his left foot," he admitted.
Newcastle 'character' impresses Pardew
"It's difficult, he's so quick and agile and works it on to his left side and you know you'll get a fantastic hit.
"That's the consistency he has. He has a really fine technique and showed how dangerous he is."
Newcastle's equaliser midway through the first-half was scored by Yoan Gouffran, who later had to be carried off after he was involved in a challenge with Kyle Walker.
Newcastle later confirmed that the striker had not broken his leg.
A statement said:
"Newcastle United are pleased to report that a precautionary X-ray has shown that Yoan Gouffran has not broken his right leg.
"Gouffran will be further assessed on Sunday by the club's medical staff."
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