DT is on the right track but maybe for not exactly the right reason. The DS18S20 does not have to run with parisitic power but it can if needed. However this from Maxim..
"Specification Differences: The primary specification difference between the two parts is the temperature conversion time: DS1820 = 500ms (max) and DS18S20 = 750ms (max)."

I believe you may also be using "count remain" improperly to signal the end of conversion. End of conversiion may be determined by issing a "Read time slot" command until the result is non zero. (Yes, it is in the data sheet!) All that being said, you can probably get by with only adding the 750ms delay after the conversion command.
Jim