Thomas is acutely aware his side face a far tougher challenge this time round.
Wales have been hit by injuries - and the rest of the RBS 6 Nations will be ready for their high-tempo, attacking style.
But he said: "The sign of a great, great team is in defending a championship.
"I relate to it like your first year of professional rugby; it is the easiest you will play, because no one knows who you are.
"But you come into the second year and all of a sudden you have got a reputation - and people come after you. That is the situation we find ourselves in.
"We know what to expect; other teams know what to expect - and we must get used to it."
Even so Thomas believes the memory of how much last year's success meant to the nation will be enough to spur Wales on in next weekend's vital opening-round clash with England.
"Everybody in Wales is still talking about the Grand Slam, and you don't want to stop them enjoying it," said Thomas.
"They can ride the crest of a wave forever, and it was great to make a nation as happy as we did.
"As players, we have to forget about it and move on to something new - but if you can make a nation that happy with one Grand Slam how will they feel if we win two?"
Wales suffered another injury blow when it was confirmed Jonathan Thomas will miss the first two games of the championship with a hamstring injury.
They are already without Brent Cockbain, Ryan Jones, Kevin Morgan and Chris Horsman - while Gavin Henson and Ian Evans are both suspended for the opening two games.
The loss of Jonathan Thomas and Evans' suspension leaves Wales with Robert Sidoli, Ian Gough and Adam Jones as the only fit second rows in the squad.
Michael Owen is an option, but head coach Mike Ruddock will prefer his vice-captain to stay at number eight where he has been so influential for Wales.
Gareth Thomas is also a concern for the England game. He played for Toulouse against Llanelli last weekend with heavy strapping on a twisted knee.