While I can't divulge much of the sale, I can tell you that when I started back in 1994, I started with a $14/month hosting account. At the time I hosted only clients that I performed web design services for. By 1996, I opened the door to clients and referrals from those clients (you had to know someone), and by 1999 it was open fully to the public.
At the time of the sale, we had 5,000+ clients, 10 staff members and grew the company on SEO and referrals (except for a $500/month Adwords budget that targeted a specific ecommerce software).
Years ago I read somewhere that when starting a business, you must determine your exit plan. Sell, Give, or Close. For me, it was going to be a Sell or Give option, and I always had a magic number in my head that would make me sell.
My wife wanted to leave the corporate world (software sales), so I taught her what I knew on SEO and we proceeded from there.
The big difference I see today in the SEO world is of course that there's very little overhead to get into the game - which is also true of Web Hosting "companies." They both still rely on one core truth - service at an affordable price. The definitions of "affordable" change depending on the work involved, the results, the industry and the market, but affordable none the less.
We have been approached to purchase another SEO company, and up for sale was the name and the clients, but not the person. At the end of the day, their reputation had been ruined through bad practices and while they had a decent number of recurring clients, the pricing wasn't in alignment with ours and would have quickly resulted in a massive drop of clients.
In the web hosting world, you can save a client easily by moving them to a new server, giving them more attention and more features for relatively the same price (be it low end $5/month or mid-range $40/month). With SEO however, most of the SEO companies I have seen for sale operate on a "race to the bottom" when it comes to pricing, and as a result, cut corners and perform black-hat in order to save a ranking etc. The damage is often already done, and may not be noticed for a few months after a sale has gone through.
Personally, I'd be very cautious purchasing an SEO company as there's limited tangible/verifiable information. Many don't keep timelogs of work performed or what exactly is performed and on what date. As a result, if the old SEO performed some blackhat work to just get them through another 2 months of service, the client could be a total loss if the work can't be reversed or caught.
I don't know about others, but people buy "us" (myself & my wife) and not so much the product of SEO. Anyone can perform the work we do, but few can perform the handholding or explanations in the same way. I'd be very interested to see what clients would continue services if the people they built the report with were removed from the equation.