You probably need to take this to Tech Support for a definitive answer. I will hazard a couple of observations.
First, the behavior you see will vary significantly by version of SAS. SAS 9.2 is much more robust about importing Excel than is 9.1.3 than is 8.2. SAS has made many improvements with 9.2.
I think that, for general formatting, SAS looks at all or some of the observations to determine type. If there is any character in the column, then SAS brings it in as text (BTW, a leading space before a number is text)
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