Apologies ozeb, I misread the breadth of the comment regarding bills. I believe you are totally correct.
However, I have seen quite a few trustees personally pay tax, accounting etc bills for their smsf and this counts as a contribution (concessional or otherwise), but this can only happen in accumulation phase. Where trustees in pension phase have made a 'contribution' (read: paid a bill on behalf of the fund) it gets a bit more tricky, but can be repaid as a short-term loan though.
Personally, like you I think, I prefer to keep things separate and only have one 'gate' in / out of the fund.
