In the following Xsl file, I have found that field values having 0.00 or 0 end up as String and not Number:

<xsl:template match="/*/*/*">
  <Cell>
		<xsl:if test='number(.)'>
			<Data ss:Type="Number">
				<xsl:value-of select="."/>
			</Data>
		</xsl:if>
		<xsl:if test="not(number(.))">
			<Data ss:Type="String">
					<xsl:if test="(.) != 'NULL'">
						<xsl:value-of select="."/>
					</xsl:if>
			</Data>
		</xsl:if>
</Cell>
</xsl:template>

If my numeric fields have a value other than 0 than they are processed as number. Thus, they will be aligned right in the spreadsheet. But, why a value of 0 makes it processed as a String?