The Australian led Spurs to the Europa League title this season - a first UEFA trophy in 45 years won by the club. The triumph also sees Tottenham handed a place in next season's Champions League.
But Tottenham's 17th place in the Premier League has cost Postecoglou his job, despite the squad's injury crisis throughout the campaign.
Vega raged on Sky Sports: "We are now in a place where a trophy is not valid at all whatsoever. The principles and the disciplines are not valued in the same way.
"What kind of inspiration or example can you bring to the future and the young talented players? Do you not want to win trophies anymore?
"In football, results count. And they won a trophy. It's unbelievable.
"The only excuse that they can come out with, is that the second season saw them have unbelievable injuries where inexperienced young talent - and Ange had to reinvent the squad because there was no backing there.
"80 per cent of the men's squad was out - when you're top centre-halves are out for 25 per cent of the season, it's impossible to be successful, with all the competition flying into it.
"And they still won a trophy? The league situation, there's an excuse."
Who would take the job now?
Vega, 53, continued: "The question is here: 'where do Tottenham want to go with their manager? Why are they now sacking someone where they can bring stability into the whole club?'
"The fans - 250,000 people went to the parade, when is the next time they will do that? They aren’t talking about 17th in the league, they won a trophy!
"We are degrading winning a trophy here. Ange had a big personality clash with the main guys in the board. Both parties were not getting on together."