Do you want them to?
There is no "view data" in Reader (AFAIK, I don't use Reader a lot), but if you distribute the twbx with an Excel / CSV / Access file, then someone could change the .twbx extension to .zip and easily get access to the data. Or they could download a trial version of Desktop and load the twbx.
There is the Worksheet > Export > Crosstab to Excel and Worksheet > Copy > Data. The attached .jpg shows where these features are located in Tableau Reader. I'm using Tableau Reader 8.0 in the example.
For the data set in the example I used, the Worksheet > Copy > Data pasted nice (as usual, thank you Tableau!) into an Excel worksheet.
export-data-from-reader.jpg 96.9 KB