Gigabit Modem Router

[#1]

Hi All
Iv been looking for a new Modem Router and thought while I was getting one It would be prudent to get one that is Gigabit capable seeing that  Im thinking of getting a NAS and a Mede8er media player which have Gigabit network ports.
While looking I saw this quote
""Why do you need it,(It being a gigabit modem router) have you got a Gigabit broadband connection?  
Normal modem/router plus a Gigabit switch is cheaper, more effective and more flexible.
(the last Gigabit switch I purchased was £13.89 delivered) """"
Which made me think and raised a couple of questions on my part. First being Am I right in thinking there is only one line speed for domestic phone and BB and every one has this line. So Is that what the above quote ment? when they said " have you got a Gigabit broadband connection"?
Or Is there a different line speed for business or how does it work?
Next is what did the person mean when they said it was cheaper to get a gigabit switch when a ethernet router that has10/100 speed  then goes into the switch which is 10/100/1000 you you will never reach the 1000 if it has to pass through the router?. And only PCs and whatever are attached via the switch will get gigabit speeds between them but if connected to the router wont. Hence whats the use other than a gigabit home network?
Or am I all wrong in how I am thinking the gigabit works?
regards Osh

[#2]

Look at it slightly differently
Connecting wired devices to a gigabit switch gives you a low cost fast network, which you want for NAS/Media
ADSL provides up to 24Mbps, Fibre up to 78Mbps; both less than 100Mbps and using a single channel/port
The modem/router sits between the two, so 100Mbps is sufficient unless it is extending the wired network to gigabit capable devices.
11n wireless may tax 100Mbps if it is 11n300/40MHz

[#3]

If you want a single unit rather than 2/3 then a router with gigabit ports is useful. However once you insert a switch into the equation you can have more than the 4 things connected to the router. As has been said the max you will get (without FTTP) is 80Mb so as far as incoming/outgoing traffic is concerned then the presence/use of a gigabit port is negligible.
However once you connect your pc/nas/why via a gigabit switch they can start transferring things faster, also even the equipment on 100Mb ports benefit if fed from something feeding them by a gigabit port.
E.g, I feed my pi form my l/t using nfs feeds. The l/t has a gigabit connection to the switch, the pi only 100Mb but it will stream 1080p with no problems, where as I has issues before on a 100Mb network feeding the same content.
Another  benefit of having a separate switch is you can connect as many devices as you want limited by the size of the switch you buy, and they are cheap and easy to upgrade and there is no need to reset up your BB connection if you replace the switch.