OK, looking at all the posts here and adding a thought of my own, here's my (or our?) answer to 'why is it so?' at Suncorp for the Wallabies:
1. Tightly tiered stadia designed solely for rectangular football formats and with seating v close to the rim of the playing field add hugely to the fan<>players connection and the utility to the team of the intensity of the fans' support for the team.
2. Equally, for the same reasons, the fans are far more intimately connected with the game and their passion and vocality is far more roused than in ANZ-like stadia. Factor 1 and 2 start to co-mingle and player motivation and fan motivation start to build up together, and there's no doubt this adds rocket fuel of sorts to the local team. (Note that the the ratio on unfilled seats in Suncorp for Wallaby Tests is probably lower than at other Aus Tests stadia, this adds to atmosphere.)
3. Brisbane's rugby fan mix is more 'cross-over' and varied than elsewhere in Australia and its clear to most of us that they get pretty wound up at Suncorp, especially if they see good, entertaining play (this was also on display big time as the Reds revival built momentum this year).
4. There's lots of good restaurants, pubs and bars right around Suncorp and this adds to the 'let's rock' factor when fans get to the game, plus more families find this and the v close proximity to Brisbane itself a real attraction of Suncorp.
5. (from me, a theory, please indulge!, you may not agree) The recent post-2003 Wallabies have generally more and more lacked what I'd call 'pre-built inner team confidence'. The sort that creates the type of all-of-80 mental resilience, 'hard mind', and self-belief that means, critically, that local fan support is not an essential ingredient in the tank come game day. If this is a correct analysis, and I believe it is, it's likely therefore that the last 5+ year Wallabies (much more so than say the ABs), will derive a disproportionately greater psychological benefit from the above Suncorp-type conditions than other leading teams gain or need. In other words, the Wallabies will gain greatly from externally sourced motivation to compensate for a comparatively lower level of inwardly available self-confidence and the motivation that can, or cannot, come from that. Accordingly, this intense, closely communicated, externally sourced motivation (in a Suncorp-like environment) adds greatly to the Wallabies inner drive and conviction, giving them the rocket fuel they in part naturally lack (or have at too low a level), and this 'fuel' turns into more points at critical stages of the games they play at Suncorp. This type of 'intense fuel top up' happens at other local stadia in Aus, but to a lesser degree given the type of stadia available for Tests.
Summary: the total set of Test playing conditions at Suncorp (factors 1-5 above) create 'the perfect storm' of Wallaby-love that works, and so a sustained and consistent high w-l ratio is achieved, in quite a remarkable manner. (And this may well be why the Wallabies have come to call Suncorp their 'spiritual home' because to a real extent that title is even truer than it looks.)
