Even if 50,000 people sent in a disk, they still wouldn't have to send out the source.
The GPL doesn't require the source to be sent to everyone that asks; it only requires that you provide the source to people that:
1) you've distributed the software to, and
2) ask for it.
Since the GPL has been used to distribute popular "Free Beer" software (i.e. GNU/Linux) it has been seen as requiring free distribution.
Castle is perfectly within their rights to distribute the source cose in this manner. Again the GPL only requires the source be electronic and machine readable.
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Even if 50,000 people sent in a disk, they still wouldn't have to send out the source. The GPL doesn't require the source to be sent to everyone that asks; it only requires that you provide the source to people that: 1) you've distributed the software to, and 2) ask for it. Since the GPL has been used to distribute popular "Free Beer" software (i.e. GNU/Linux) it has been seen as requiring free distribution. Castle is perfectly within their rights to distribute the source cose in this manner. Again the GPL only requires the source be electronic and machine readable.