Yep, it's right. As long as you qualify for your company's enhanced sick pay, and you haven't used up your sickness entitlement for that year. To not pay you sick pay in your notice period would be discriminatory. I would imagine the reason that not everyone's doing it, as you say, is that most people are decent and hardworking and would feel guilty and wouldn't want to jeopardise their reference. And it's not actually that easy to get a sick note if there's nothing wrong with you.
It shows how much I know - I didn't realise there was such a thing as sickness entitlement. Is that a standard number of days with every company? How about people who only get SSP? and what on earth is enhanced sick pay?
I've only worked in retail, but every company I've worked for has an absence policy, whereby the longer your service with the company, the more sick time you get in a year (usually capped after 40 days) and your sick pay goes up too (so all unpaid in first year, for example, going up to full pay after 3 years - that's what I meant by enhanced, probably just my company jargon, sorry!) It kind of works in the same way as maternity pay, IME. But that's just retail, which is notoriously underpaid and tight for benefits! SSP (I think) can only be claimed after 3 days off in a row, and any company sick pay you receive would supersede that anyway. Most sickness doesn't last 3 days - I've been managing staff fir 10 years and either they drag themselves back in and infect everyone else, or it's a duvet day. (I'm being flippant - I do believe most of my staff!)
There is no such things as any entitlement to sick pay, other than SSP. If a company chooses to offer enhanced sick pay arrangements, they can put conditions on those, and could also put a condition on it that they will not pay out during notice periods. It's not 'discrimination', as 'people working their notice' are not a protected group.
Having said that, most companies who have enhanced sick pay don't have a condition about not paying it during notice period -partly because it's unnecessary. If the sickness is genuine and supported by a doctor's note, why would they not want to pay it if they are generous enough to offer enhanced pay in the first place? They would have mechanisms in place (usually) to allow them to withdraw it if the sickness is not genuine.