Severance Package Negotiation Question in VA

I was forced to part ways with my employer (fortune 500 computer software company)two weeks ago, after HR asked me point blank if I had submitted a report concerning ethical and moral violations. I said yes, because they trained us to do so and they'd eventually find out anyway. I didn't expect to be terminated for following protocol. Anyway, they offered a 3 month severance package. However, I also lost out on 20K in company stock which would have vested in one year and a great telecommuting job, which are very hard to find. I elected to hire a local attorney who wrote and sent them a letter with a counter offer. My former employer responded with a response acknowledging receipt of the letter and that they would be sending a "substantive" response within the week. The week has come and gone as of Friday and we haven't heard anything back yet.

I'm curious if this is standard in severance negotiation. Is this a tactic that is often used by employers in these situations?