He is an absolute gold mine for sponsors, so that would make it easier for him to get a drive. Equally, it must play on his mind too. He turned down a test for Team Lotus because Ayrton got his first win with them (well, in name only).
Going a little off-topic, when it comes to drivers with a lot of sponsorship money behind them, I wonder whether they do feel they are really only there for the money, and not because they are necessarily good enough. At the extreme this season is Karthikeyan, who (and I know this sounds hypocritical with regards my last comment!) isn't exactly showing any kind of pace at HRT, relative to Liuzzi, and I'd argue his driving doesn't warrant his seat. I guess the jury is still out on Maldonaldo, although his last couple of performances have been promising, so I'll reserve judgement on him just yet. Whilst the likes of di Resta are purely there on merit, and I'd say he does deserve his seat based on performance.
Back (slightly) on topic, I remember when I was listening to the FP1 commentary on five live, that Senna said that Karthikeyan had come to him for tips around the circuit, and just remember thinking, "No offence, but there are a good number of drivers better placed to advise!" The number of ex-champions at Monaco, I bet one of them would be prepared to offer advice.