The Westpac profit for the second half of its financial year seems to make Westpac the odd bank out in the reporting season that drew to a close yesterday. Westpac's banking businesses, in Australia, at least, are not generating the revenue growth of its peers.Westpac reported growth of only five per cent in net interest income in the second half, versus the first half, in its "Westpac Retail & Business Banking" division (the business that could be termed the "old Westpac", before the merger with St George Bank a little less than a year ago).Growth in net interest income at St George Bank, now a division of Westpac, recorded growth in net interest income of six per cent in the second half compared with the first half.National Australia Bank reported growth in net interest income of nine per cent for its Business & Private Banking division in the second half over the first. NAB's retail bank reported growth on this item of 11 per cent.ANZ recorded growth in net interest income of eight per cent in Australia in the second half over the first (and splitting the different growth rates reported for the "Australia region" and the "Australia division").Using growth in net interest income as the basis of comparison leaves out the harder-to-compare operating income from fees and trading. In the case of Westpac this was lower in Australia, given one-off increments in the first half (tied up with changes in credit card rewards).Supposedly Westpac is doing splendidly in key product markets, such as home loans. And the bank says there is no shift in customer margins (with margin increases coming from broader balance sheet management).The bottom of the ladder increase in net interest income for Westpac at a time of well-above system growth on home loans and also deposits needs some explanation.One analyst at the investor briefing yesterday, who raised a question on revenue in the context of projections of moderate loan growth next year as well as factors restraining fee income growth, received a pretty woolly answer from the managing director, Gail Kelly. "Deepening and strengthening relationships," was the guts of the answer.One guess, amplified in the next article, is that Westpac's shaved margins on home loans by more than was appreciated in order to achieve its growth goals.