Rather, as some newspapers later reported, the President's involvement was necessary because the Lokpal's expenditure will be charged to the Consolidated Fund of India. Article 117 (3) of the Constitution requires the President to sign-off when a bill includes such a provision. Yet, contrary to the news reports, the President did not "assent" to the Lokpal Bill before it went to the Rajya Sabha. Presidential "assent" is only granted after a bill has been duly adopted (or deemed to have been adopted) by both houses. Rather, the President had only "recommended" that the Rajya Sabha consider the Lokpal Bill as passed by the Lok Sabha.
The Article 117 (3) requirement applies when either house of parliament (not just the Rajya Sabha) considers a bill involving Consolidated Fund expenditure. Accordingly, a Presidential recommendation had already been obtained when the government introduced the Lokpal Bill in the Lok Sabha earlier this month. Due to Article 117 (3)'s wording, a separate recommendation was necessary before the Bill could be sent to the Rajya Sabha.
Interestingly, the President's communication to the Lok Sabha also cited Article 117 (1), which requires prior presidential recommendation for "Money Bills." These bills are defined in Article 110 to include those involving expenditures charged to the Consolidation Fund. The reference to Article 117 (1) was omitted from the presidential recommendation to the Rajya Sabha ostensibly because, as a Money Bill, the Lokpal Bill could only be introduced in the Lok Sabha.