cant find the link anymore, but here's one showing clubs' net spending since 1992 that backs it up to a large degree.
http://biawc.110mb.com/
during this time period, liverpool have actually spent more than Utd.
Net Spending 1992 - 2007
-------------- Bought----------------Sold----------------------Total Spending
Chelsea-------486,720,000 --------145,050,000----------£ 341,670,000
Liverpool-----309,040,000 --------134,230,000----------£ 174,810,000
Man Utd------337,700,000--------177,340,500----------£ 160,359,500
Newcastle----275,446,000--------133,225,000----------£ 142,221,000
Arsenal-------216,930,000--------155,054,000 ----------£ 61,876,000