It's not clear that this is true. According one analyst:
http://www.herring.com/insider/1999/1108/inv-msftvalue.html
if you split Microsoft and valued each piece based on revenues (presumably
applying the proper multiplier for each segment), you'd get:
platforms, $57 billion
applications, $55 billion
Internet pieces, $245 billion
cash on hand, $18 billion
unearned revenue, $4 billion
or less than $400 billion, vs. $450 billion current market cap. The article
makes the point that Microsoft should not be compared to Standard Oil or
AT&T because its assets (installed user base, brand, management team, etc.)
are worth less when divided.