"At grade A, the gap between Wales and England is slightly larger in favour of England unfortunately, so maybe there's a slight concern there that with the very highest level of ability - the Welsh statistic is falling slightly bellow England."
Mr Pierce said this was part of a wider picture with the difference between achievements of girls and boys.
The WJEC said girls made up 56.0% of A-level entries and, in general, continue to perform better than boys with for example, 54% of subject entries for girls gaining grade B or above compared with 47% for boys.
However at AS level the board said there was an encouraging improvement in the achievement of boys this year, with a narrowing at all grades of the gap between their results and those of female candidates.
This should be reflected in an increase in the number of male students taking A levels next year it said, whereas the relatively weaker performance of boys at AS last year will have contributed to the A Level entries for boys remaining static this year.
Cyfarthfa High School's head boy and girl both achieved across-the-board A-grades
An increased number of pupils were taking the exams with a total of 36,836 A-level subject entries this year.
The most popular subjects at A-level and AS in Wales are English, mathematics, history and biology, all of which attract over 2,500 entries at A level and over 3,000 entries at AS.
The WJEC said after falling levels of interest in the sciences in recent years, mathematics and chemistry showed some growth at A level this year and there has been an increase in the number of candidates for physics at AS.
Students taking the five-year-old Welsh baccalaureate also received their results.
Based in 18 schools and 13 colleges, the total entry for the Welsh baccalaureate advanced diploma in 2008 was 1,857, of whom 1,654 (89%), completed the programme, a significant improvement on last year's figures.
A total of 1,186 candidates were awarded the Welsh baccalaureate advanced diploma, representing 72% of the 1654 who completed the programme.
Education Minister Jane Hutt said added her congratulations for the "excellent" achievements.
"I was particularly pleased to see the increased participation rates and great results that have been achieved, for example, in maths and ICT.
"The hard work of students and the support they receive from teachers and parents has once again paid off and everyone involved can rightly feel proud of what has been achieved," she added.
NUT Cymru secretary David Evans said improvements were partly because there was no longer any restriction on the numbers who could pass, as well as "significant progress" being made in raising achievement in under-performing groups.
He said teachers were also teaching more effectively and pupils were working extremely hard.
Mr Evans added: "Let's celebrate the success of our young people and our schools. All too often we seem to live in a culture where moaning and complaining are the norm and that the only news worth printing is bad news."
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