Section A39 is concerned with the applicant spouse's ability to become self-sufficient, and that the arrangements in place for their care and maintenance do not include reliance on social assistance/welfare. So, while there is no income requirement for sponsoring spouses, you do need to show that the person can become self-supporting and that there are arrangements in place to care for their basic needs (food, clothing, shelter), otherwise the applicant MAY be deemed inadmissible for financial reasons.
So, what spousal sponsorship does not require is a minimum necessary income. You still have to show financial admissibility. You can't be denied the right to sponsor because of a lack of income, but your wife can be denied if they don't think the two of you can support yourselves without needing welfare.
Alright that makes a lot of sense. Thank you for all the info it clarifies a lot for us.