Roberts made his Games debut 12 years ago and has won 11 gold medals in three appearances, including four golds in Beijing in 2008.
However, an untimely bout of pneumonia meant he failed to hit his qualification criteria at the British Gas Championships in London earlier this year and this weekend's British International Disability Swimming Championships in Sheffield.
"The rationale behind the selections was entirely performance driven," said British Swimming's disability performance director John Atkinson.
"Our selection policy, and qualification standards, were widely published and we only looked at athletes who we considered had medal potential in London.
"Dave unfortunately has been plagued by injury and illness, going back to 2009. Because of that he has not been able to demonstrate required results. For example, his best time in the 50m freestyle, from the January 1st 2011 to the current day, would only rank him seventh in the world.
"I talked to Dave this morning just before the announcement was made.
"He was obviously disappointed but he's looking ahead to what the future holds. We talked about how hard the last four years have been and we recognised that has been the issue that has prevented him from swimming as well as I would have hoped to.
"He'll now have a period of some reflection to consider what he does next."
Double Paralympic and ten-time world champion Ellie Simmonds, 17, is the star name of 16 swimmers named in the squad, while a further 26 hope to have their selection confirmed by the British Paralympic Association once the International Paralympic Committee's slot allocation has been formally made in early June.
The squad includes husband and wife Sascha and Nyree Kindred and two pairs of siblings, Oliver and Sam Hynd, and James and Emma Hollis. It also contains Jim Anderson, 49, for whom London will be his sixth Games and first-time Paralympian Chloe Davies, who will be just 13.
"We have a great mix of youth and experience within this group and with 45 percent of the athletes preparing to take part in their first Games," added Scott.
“We will have the chance to get together as a team in Majorca to get some excellent training under their belts before the final stages of preparation begin.
"I am excited as we move into the next phase in our Paralympic cycle and I will be looking for the athletes to improve on their performances between now and the Games.”
Swimming has historically been one of best medal deliverers for Great Britain - the team won 41 medals in Beijing, 11 of them gold, finishing fourth on the swimming medal table. This time around, Atkinson is targeting between 40 and 50 medals from the 148 events, split across 14 different classifications.
“I have worked really hard for the past four years to qualify and I couldn’t be happier now I have done that," said Simmonds, who will go for gold in up to five events.
“Beijing was really special for me but I think walking out in front of 17,000 people and hearing them cheer us on will be even better. Competing in front of a home crowd last month was amazing and I can’t wait to do it again.”
James Crisp (Sheffield), Jessica Applegate (Great Yarmouth), Jonathan Fox (Cornwall), Claire Cashmore (Leeds), Oliver Hynd (Kirkby-in-Ashfield, Nottinghamshire), Chloe Davies (Midsomer Norton, Somerset), Sascha Kindred (Hereford), Heather Frederiksen (Leigh, Lancashire), Aaron Moore (Trowbridge, Wiltshire), Rhiannon Henry (Manchester), Andrew Mullen (Glasgow), Susannah Rodgers (London), Matthew Walker (Stockport), Hannah Russell (Chertsey, Surrey), Robert Welbourn (Swansea), Eleanor Simmonds (Swansea).
James Anderson (Broxburn, West Lothian), Gemma Almond (Shrewsbury), Jack Bridge (R) (Preston), Charlotte Henshaw (Mansfield, Nottinghamshire), Josef Craig (R) (Tyne and Wear), Emma Hollis (Epping, Essex), Graham Edmunds (R) (Swansea), Elizabeth Johnson (Bath), Sean Fraser (R) (Manchester), Natalie Jones (Chorley, Lancashire), James Hollis (R) (Epping, Essex), Nyree Kindred (Hereford), Sam Hynd (Swansea), Harriet Lee (Peterborough), James O’Shea (Newcastle), Amy Marren (R) (Hornchurch, Essex), Daniel Pepper (Stockport), Natalie Massey (Stockport), Benjamin Procter (Newquay), Stephanie Millward (Swansea), Craig Rodgie (Dunfermline), Lauren Steadman (R) (Huntingdon, Cambridgeshire), Anthony Stephens (Highbridge, Somerset), Louise Watkin (Leigh, Lancashire), Matthew Whorwood (Newquay, Cornwall), Thomas Young (Manchester).