The above post is excellent and coresponds to my recent experiences with cable.
I have used and seen both DirecTV and cable and the cable with DVR is of at least the same quality as DirecTV. The cost for DVR service is 10 bucks a month from Comcast and Cox as well as others - depends on your market.
But, the big deal is that you are not BUYING the equipment in these volatile A/V times where new technology is replacing old every few years. So, as new technology comes along you can call your cable company and start pestering them for it. They may be a little slow, but you will often get the latest and greatest for your same 10 bucks a month.
Oh: Your Replay TV is NOT HD compatible! You can use it to record shows I imagine, but do not use it for general viewing of content as the lack of HD inputs on the box completely destroy the quality of your viewing and take it back to standard definition TV. Or, about 1/4 the quality of what your cable box puts out.
I was thinking of getting a DVD recorder recently... But, at about $300.00+ for one with integrated hard drive, I realized that I could simply rent a cable box with DVR for 10 bucks extra a month and it would take about two and a half years before I would have had that DVD-R paid for... plus the DVD-R wouldn't have handled my HD recordings which are about all I ever record these days.