Some major points to consider:
1) Really good marine use foul weather gear will have things like fleece lined high collars and heavy duty hoods to take the spray and rain and keep it off your face and neck.
2) The marine gear has retro-reflective patches, which make the people far easier to spot, especially in a MOB situation at night. Regular foul weather gear is generally not as heavy-duty, chafe resistant, or waterproof as marine use foul weather gear.
3) Marine use gear also generally has dual sealing cuffs on the sleeves that will allow you to raise your arms but prevent water from coming down the sleeves when you do so.
4) The pockets on most marine foul weather gear is fleece lined for warmth. The jackets are probably better ventilated for the wetter environment than standard gear.
5) Regular foul weather gear also doesn't come with the choice of an integrated safety harness
, which is available on many of the marine specific foul weather gear.
This is one instance where the stuff you get for the marine specific use is really far superior IMHO to the stuff that you get at Lands End.
If you're only going out day sailing in fair weather, then it really won't matter...but if you're planning on doing any real sailing, then it will make a huge difference in your ability to stay warm, dry and comfortable. Getting soaked and staying wet, on a long passage, is a good way to get hypothermia and make stupid mistakes that can cost you your life. It is also uncomfortable and miserable.